Ok, I know this guy has heartbreak written all over him but please help me understand

I casually dated a guy that I met the last 2 weeks of college for about 2 months (LD after the 2 weeks). He was not over his ex girlfriend at the time (not recent btw) so that's why we weren't official. I know, red flag.. but he talked to me for hours everyday, confided things to me , and always wanted to spend every minute with me.He often times seemed to genuinely miss me. We did have sex by the way. Basically, everything seemed perfect but I needed to break things off with him-he went on dates with other girls. He was shocked and told me about this new girl he was hanging out with saying she wanted to date him and he liked her but was holding off/confused because it "didn't feel right with what we had going." Now, the next day after the break up he starts dating her (he's known her for 3 years btw) and 8 days later she becomes his official girlfriend. He has always been the serious type and I was the 1st non girlfriend he had sex with.

Now, that day he was talking online with me while she was sitting RIGHT next to him on the couch.. why he didn’t say he was busy is beyond me (idk if she knew or not). Though, he said he was going to call me later that night and never did. Also, after only a WEEK of them dating.. he ims me on fb the very second I sign on saying eagerly "how are you?" Now, 2 weeks after that he liked one of my statuses on fb. Now, today he said “ we will have to get lunch or something and catch up" He is a nice guy who wouldn’t intentionally go about hurting anyone. I just want to know if he's in it for backup sex, just being friendly and is serious about the new gf(do you think he is?), or if he's confused/still into me so I can stop wondering lol. The last 2 times I've seen him on fb he didn't I'm me btw.. but I don't know if that means anything.

I don't know, part of me wants to believe he's just confused about what he wants and that's why he's keeping me around as a friend. With the ex he wasn't over he remained very good friends with her while he had a girlfriend so I make myself think he's doing the same thing.. but at the same time I feel like I'm kidding myself because she was his 1st true love and they dated for a year and I was just some casual 2 month. I think what would hurt the most is if I found out he was doing this because he feels sorry for me and just wants to be friendly out of guilt.. I hope that's not the case. Is he really into the new girl though and is just being nice to me?

I'm at a point where I still hold out hope for him and think about it but I am happy and able to be interested/get involved with other guys. It is apart of my daily thoughts, but it's not affecting my life negatively if that makes sense.

I just want to know if he's in it for backup sex, just being friendly and is serious about the new gf(do you think he is?)
Well in my opinion, Yes. he knows what he wants. He is selfish. he is just thinking bout himself, 2 girls, one official and another one to hang around and have sex. He is concious of what he is doing. he has a girlfriend, and you. Both of you girls are the other.
he was with u and went to her, and now he is with her and with u at same time. If u dont love this guy, let it go. If he is not able to leave his girlfriend and take a chance on you, he is not gonna be good for you.
You deserve better than just some talk and sex. U dont need to be a back up plan.
I bet there are plenty of single guys out there wanting to have a nice girlfriend and is single.
Good luck:)