Fell In Love With Neighbor, Doesn't Get Along With Roommate

Let me start with the set, setting and characters. I live in an apartment with a single roommate. We've been friends since early high school and have always got along. Directly next to my apartment is another in which a lady (same age as me) lives with her roommate. After 8 months of knowing this neighbor, I started dating her, going against all instinct that this may be a bad idea. I know that I am a dumb ass and I normally wouldn't do something like date a neighbor, but no girl has ever made me feel the way she does. She is one of a kind and we just click. We've been dating for 5 months now and it has been absolutely amazing.

Now the issue, I'll get right down to it. One day I'm sleeping at said lady neighbor's house. It's 8 in the morning and a rather abrupt knock raps at her door. It's my room mate and he is furious. He states someone stole a few items of his and he thinks it's me. I am completely dumb founded, as I would never do this. I'm a very cool headed guy and my initial reaction is not to flip out, but to talk logically and cool him off.

I accomplish this and I ask for him to apologize to our neighbor for waking her up in the morning. He does, albeit rather half-assed. She then proceeds to shout at him for coming to her door crazed in the morning, accusing me of something I would obviously never do. She chases him out of the house.

She stood up for me, which is very sweet of her, and this is part of the problem which I will get to.

A few days past and she brings to my attention that things are now very awkward between her and him. I need to do something about it. This however is a very sticky situation for me. He is my best friend of 15+ years and roommate. Though he did accuse me of stealing, he hasn't been right recently. He's very stressed and constantly deals with a lot of physical pain due to a bad automobile accident. He also recently got over a pretty bad drug addiction.

A month passes and I don't speak to him about it. She starts to get frustrated that I don't stand up for her and that I don't raise my voice to him in anger for her, like she did for me. She feels awkward coming to my house and running into him, in which they don't say a word to each other. Tonight I decide to talk to him calmly, just to understand his side better. He basically informed me he doesn't give a shit and just generally does not like her. Me being a pansy, worried that I might stir shit with my roommate and make things awkward for my self, in my own home, don't take it any further.

I make the mistake of talking to her and telling her that I don't think there is anything we can do. Yes, I'm a total dumb ass. She is now totally pissed at me. I ask her to understand my situation a little better, but she just doesn't. She seems to just be upset at the principle that I didn't loose it for her and stand up for her, when she did for me.

What is the best way to go about this my friends? I'm honestly falling in love with this girl, she means a lot to me. And my roommate has been my best friend, though it seems like he may have lost a few marbles recently, he is still very close. I don't want her to think I'm some pushover who doesn't have the balls to fight for her. I would instantly if it was any other situation, honest. I also don't want him to think that I'm letting some girl just control me and ruin our friendship either. Should I finally approach him and really probe to get some kind of resolution out of this? Or should I just make her deal with it?

My gut tells me to get up and talk to him. Let my anger flow if it needs to and just get down to the bottom of this. I just want a little advice first before I do something even stupider.

TL;DR - I fall in love with neighbor. Roommate/best friend knocks furiously on neighbors door at 8am to find me and accuse me of stealing. Girl friend stands up for me and yells at him. She begins to feel awkward around him and in my house. She wants this resolved and expects me to do it, because I never stood up for her. She feels that I don't really care about her because I can't put together the courage to face him about it directly. I don't know what to do!

Please help reddit. If anything isn't clear, let me know and I can elaborate. Again, I know I've made some stupid choices, but it's now time to deal with the results of them.