This is my observation (through a story of a period in my life) of how different people and personalities interact in relationships and friendships and how they affect one another

My best friend (female) and I met new friends in the first year of college (6 years ago) - we were a small group of 7 friends, boys and girls. I never had a crush on any of these guys because I didn't feel we were on the same wavelength, but as friends, they were (at least most of them) a great laugh. There was this one guy that was really ambitious in studying and never had any grade below an A (even in college). He had a big ego. He was the only one that I didn't get along with at all. When I meet someone new, I always try to forgive them their faults and am very tolerating at first, but when someone crosses the line, I lose my inhibition and say what's on my mind. This guy with the ego problem thought everybody liked him (in fact many people didn't). One day my best friend and I met him by accident in the town and he suggested that us 3 go for a drink. It was spring, it was very hot and I have a problem with low blood pressure at these times so I nearly dozed off in the big wide comfy chair in the coffee shop. I didn't notice that just the tip of my knee was touching the tip of his knee because I threw all my limbs as far apart as possible to cool down. But apparently he noticed it and thought something big out of it, and suddenly started to move his foot over mine, he put the whole foot over mine. Of course my best friend couldn't see what was happening because she was sitting across the table. I found it really distasteful and hastily moved my foot away. He looked at me like he was a bit mad at me. I tried to ignore and keep a poker face. I couldn't wait till we all went home, but when we departed he asked me to come to his place before we go to our friend's birthday party because we could go together since he is close to our friend. I said sure (because my best friend was with us), but I didn't contact him that day, I pretended I forgot. At the friend's party, he danced with every girl except me, as I avoided dancing with him, he tried to make me dance with him in two occasions but I said that I don't like dancing (actually I love dancing, but better alone than with the wrong person ). He tried to make me sit next to him and than tickle me, luckily my phone rang so I could go away and answer it. At the end of the night he had a really rude outburst at me, in front of everyone, and everyone was shocked because they didn't understand why did he react like that. He said he likes playing strip poker. And then he suddenly looked at me and said "I would strip you naked in no time". And when he saw the faces of our friends, everybody had the "why did you say that"-face. And just a reminder - I don't dress sleazy. I like feminine elegant clothing but not too revealing. Then he added fast "No no we are just good friends" with a fake smile and came to hug me. And exactly after saying that, he started talking about his new girlfriend that he will just actually start dating (nobody knew he got a new girlfriend, and honestly i think, nobody cared xD). This was his 3rd girlfriend.
From that day on, I knew we were never going to be good friends because our personalities are so much different and not in that ying-yang complementary sense of different but more like not compatible at all.
As I said, our group of friends met together regularly, I met my boyfriend soon (we are still dating today, 6 years together). I didn't know my boyfriend and this guy were friends in highschool, and when I found out, I nearly didn't go to a first date with my boyfriend because I thought "well if he's hanging out with that guy, then he must be the same type of a personality". But I saw that they were actually total opposites. My boyfriend is a very warm, loving, tolerable personality that you wouldn't ever want to hurt because when you look at him, in his eyes, you see all the positivity that reflects from his soul.
So, this guy brought his girlfriend one day so we could all meet her, she is honestly a nice person as far as i knew her, quite good looking, very subtle, non dominant, has a smart sense of humor, tries to please everybody. She was very much in love with him. When we were all together and his girlfriend was around, it was the only time he was completely normal with me and we could actually have normal polite conversations. But in college, all these years, he was always subtly hitting on me, he wasn't allowed to touch me because I said I hate hugging and touchy feely people. Once there was only one spare place to sit, and he looked at me and said "if you were my girlfriend we could both sit on the chair, you could sit on my lap". To which I sarcasticaly responded "you are sooo funny." Anyway, many situations like these (especially when we were alone)...
Also, I know my best friend was in love with him this whole time (despite having a boyfriend the whole time) but she didn't want to tell me, and we started drifting apart because she started seing me as some kind of competition - but she didn't see she was the only one competing for the "prize". She is generally a very smart (in IQ sense) person and also very modest, too modest and too good for this world. Always trying to please other people and never putting herself in first place and I told her that many times. And she always praised and pleased this guy and started constantly organizing gatherings at her place at which I stopped coming because I felt uncomfortable knowing the situation and still having to socialize with her boyfriend, this guy's girlfriend, seeing them all being very friendly but tension underneath the surface. And here's me being too honest, telling everything to my boyfriend about his "friend" hitting one me, on my best friend, even on some other girls.
One day when this guy asked me will I come to his birthday, I said to him that I wish him a happy birthday but that we are not such good friends (after 5 years of knowing him), more like superficial colleagues. He said ok like he didn't care at all and I was happy that I didn't offend him and it turned out good. The next day I found out that he was outraged (and he said what I have told him to his best friend and another friend) and that he was mad about it. He started ignoring me, or giving me clear signals that I don't exist - like he comes with something and shares with everyone and ignores me, he asks everyone except me to do some activity with him, and he always did that in front of me. Actually that was the first time I was finally at peace because he really left me alone xD I also told my best friend honestly that if she liked "someone" else, then she should end the relationship with her current boyfriend because they were together for years and it's not ok to put up his hopes of future with her. She listened to my adivce and broke up with him and didn't tell me about it. Then she started socializing more with this guy and his girlfriend beacuse she was sad after the break up and after half a year he broke up with his girlfriend and started dating her (my best friend). By this time it has passed a few months since I told the guy that we are not friends and never will be good friends because of our different opinions and personalities, and I spent much time apart from our friend group, I basically excluded myself from the whole situation and started going out more with my boyfriend and his friends (from a different college). My old friends told me that he urged them to erase me and my boyfriend from their friend circle on social networks.
There were numerous occasions where this guy talked about my boyfriend as if he was some kind of inferior person, and once he even told my boyfriend's family secret that he knew I didn't know in front of me and my boyfriend who was then so embarassed and distressed, thought I was going to break up with him for not telling me, but I understood why he didn't want to tell (we just started dating then, he didn't want to make a bad impression), I forgave him then, and from that day on, we keep absolutely no secrets from each other and are even more connected.

The last "soap opera" moment was when a few months after he started dating my best friend, he made her wait for me with him after class, to try and talk and make up beacuse "it's such a shame, we were best friends and we don't hang out any more." She wasn't keen on doing that because she said to him that we talked that day (we did) and said everything needed to be said. We aknowledged our differences and I was honest with her and said that we drifted apart, and I knew she was in love with him this whole time but kept lying to me for years, and I was honest the whole time with her about his behaviour towards me, so I don't feel like we are honest friends any more because honesty goes both ways. And I told her I also don't find it correct that she was trying to be good friends with this guy's (now ex)girlfirend the whole time, but wanting to date him at the same time and working on that. When we were pressured to confront again after class, he did all the talking, and my best friend (his girlfriend) was looking sadly at the floor, feeling uncomfortable. He said that it is sad that my best friend and I are not best anymore, and that he doesn't understand why my boyfriend doesn't want to talk to him. He asked why he doesn't want to? Then I became pretty much straightforward and told him "remember when you told me about my boyfriend's secret in front of me and how you talk rude about him?! Do you want me to discuss that in front of your new girlfriend or shall we go private!? That's why he doesn't want to talk to you!" And then he all of a sudden went silent and said quietly but clearly irritated "fine, it seems like there's no use of trying to make you two reconcile." I said "Good, you get it. Ok, nice, I gotta go now, see you in class, bye!" I turned my back and went my way.

2 years later they got married. Actually I think they are a very good match, they are the ying yang type of opposites. Dominant and submissive. Irritative and calm. Always trying to impress, always being modest. Big ego, small ego. One leads, the other mostly follows, but together make a functional team.

So basically, I lost a life long friend, lost my social group (the whole group stopped hanging out after this), but kept my boyfriend and hopefully we are heading the same direction in life.