Signs he's cheating, or that I'm paranoid?

I'm not sure if I'm just letting my trust issues get the better of me or if I have a reason to be suspicious. My fiancé has a chronic illness that was just diagnosed last year, so he started working online from home. So he's there alone every day, a lot of the time at the same times one of our attractive female neighbors is. I come home and see most of the time (from the cars in the parking lot) that he and her are the only people there a lot of the time. Anyway, he and I were leaving our apartment about three months ago and as we walked to our car in the parking lot I noticed that he walked up to our neighbor's car's passenger side door instead of ours. Her car is a lot bigger than ours and is white while ours is grey, so it's not like he mistook her car for ours. He says he was just really stoned and not paying attention, and we had been smoking pot right beforehand.
I also brought up how loud I've noticed she is (slamming doors, blasting bass all night) and he mentioned her having a bad stereo system in her car. I don't know how he would know this, he says he looked out our window one night and saw what he thought were her brake lights in the parking lot with loud bass coming from it and that's how he knows.
Also he has started complaining about how loud she is a lot more in the past month or so, and we've also been having sex a lot more in the past month. I thought maybe this was a sign he was having sex with her and broke it off? Or could it be a coincidence? Our other neighbor that was also really loud just moved out, and I think maybe he's just starting to realize a lot of the noise he's been hearing is the female neighbor, which he was blaming on the male neighbor that recently moved. So that's a believable reason he would just now start complaining about her. Plus why would he complain about her when he knows she might out their relationship to me if I complain to the leasing office about her or call the police for a noise complaint. She also has a boyfriend so that could be something that would deter her from ratting him out if he were to **** her over via me somehow.
One more could-be suspicious thing is that a white mark showed up on our car door a couple months ago, and it was obviously this female neighbor that parks next to us, and I said that's what I thought had happened and he vehemently disagreed with me, even though it was obvious from the position and color of the mark that she had done it when opening her car door... I thought maybe he thought she wouldn't do that because of their relationship?
Last suspicious thing was that he came inside one morning and told me she had talked to him in the parking lot. He had been lying under the car and she came out to go to her car and asked if he had a flat tire...which is a stupid question because anyone with eyes would have noticed the huge new dent he was working on. I thought maybe he was trying to cover up them talking to each other outside, incase I had seen them, and I would have clearly seen if I had looked out the window during that time.
One thing that I thought was pretty convincing of his innocence, which is why I'm so confused about this, was about a month ago I said I was gonna go ask a different neighbor that we're friendly with if he'd seen Laura (female neighbor I'm suspicious of) in my missing high heeled shoes, because at that point I was convinced he'd given a pair of high heels I'm missing to her...for some reason... Anyway when I said the name Laura he looked at me with what I thought was genuine surprise or confusion and said "who?? I don't even know who you're talking about". He has no reason to know her name as as far as I know they only talked that one time in the parking lot, so that's part of the story that makes sense, unless he was quickly lying.
If these things are suspicious to others, how do I find out for sure what's going on? I'm ashamed about this, but I already crept on his phone and facebook and didn't find anything, but there are a lot more ways than that to comminicate these days, not to mention that she's just a flight of stairs away from him.

I'm sorry this post was so long. I hope I can find some help anyway, because it's ruining my relationship, self confidence, sleep, everything. Thanks.

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OH and this is really the last thing--about two weeks ago I walked past her on my way up the stairs, and she completely ignored me whereas she's always been friendly and said hello all the times before. Thought maybe they had broken it off and she blames me? Why would she be trying to talk to him in the parking lot and completely ignoring me all of a sudden?

This sounds like paranoia and to be honest, I think you're at the point where you need to look into some therapy.

You are over-analysing snippets of information that are entirely benign - most people wouldn't even notice them - and drawing grand conclusions which validate your fear. Why on earth would you think your partner would give the female neighbours YOUR shoes? That's absurd. And you even went as far as asking your other neighbour...who didn't even recognise the name 'Laura', if he's seen her in your shoes...I mean, would the guy have even noticed the type of shoe she was wearing even if he had seen her around?

What would quell your paranoia? What if you locked your boyfriend in the apartment all day and installed spy-cams just to make sure? Doesn't sound reasonable, does it? But short of doing something absurd like that - you have to accept that other people (and other women) will ALWAYS exist. It's up to you to trust your partner. It's also up to you to get help for yourself because living like this can't be easy - for neither of you.

Maybe if you stop smoking pot, you can get rid of your paranoia, lol.

On a serious note, why on earth would you suspect your boyfriend to be cheating on you based on the incidents you mentioned? Giving the neighbor your used shoes? Who would do something like that?

Woman, get some help and stop smoking pot. To answer your question.... NO... your boyfriend and neighbor don't Seem to be cheating on you.

Call a private detective and pay him to watch, within your apartment building, your bf's movements from the time you leave in the a.m. until the time you arrive back home. Maybe a weeks worth of proof that the bf is not doing anything but working away and staying inside his own unit will calm your angst and insecurity. If he is sneaking up the stairs, the P.I. will let you know and you can tell us here "see I told you I wasn't paranoid."

Then after that... pay for therapy to get you past your inability to trust.

I don't see anything suspicious here tbh.. are there any changes in his behavior, how he treats you? There are usually signs of cheating and red flags.. i see nothing here. I think your paranoid

I met a girl on the online-dating site. We started communicating and then I came to her country. Now I'm waiting for her visit to the United States but she has not been removed from the dating site yet. Says that it is difficult because of the contract with the agency. Somebody used mymagicbrides.com and is it true?

I don't think its suspicious...I think you have nothing to worry about. You'll have to start trusting your partner more and don't doubt him so much.

Yes, paranoid. Yet if you can't shake it as someone above mentioned for peace of mind, hire a Private D and get your answers.
Though I must say, it does sound like your going a little over the top with your suspicions, but if they do not subside, get proof either way. OR, buy something from a spy shop and do it yourself. It sucks to feel the need to spy on our partners but if your gut is feeling unrest, you must do what you can to remedy any unrest. You'll either find out A:it's all in your head and you've nothing to worry about aside from your feelings of mistrust or B: you were right to be concerned.
Either way, you got to find out.

Ya I think it's the pot talkin............