Ok so I'd like to apologize firstly for the length of this, but so much has happened and I really am so overwhelmed that I don't know how to cut it down at the moment. But any help would be appreciated. I'll post a tl;dr at the bottom, but I really do have a lot going on as stated below.

So Im having this problem with two girls. Basically I'll start from the beginning. I met this girl who I'll call girl A about 6 months ago. We talked, I had a crush on her, naturally we started dating. Eventually it became a very serious relationship in contrast to how little we were together. When we first met she made me feel extraordinarily happy and like nothing else mattered. She pushed me to keep going forward and to do better. Eventually it came to the point in which we ended up living together. We had the occasional fight, but nothing too major until about 2 months ago (4 months into the relationship). Around then she began to become more emotional, starting fights over small things or losing her temper and overall getting over-emotional. When I asked for some me-time to focus on myself as an individual she'd shout and guilt me about not wanting to be with her. When she'd shout at me about what I'm doing wrong (Often things like not wanting to go out after a long night) I'd naturally defend myself without shouting and it would start a fight about how she'd say I'm not allowing her to have emotions or vent. I tried telling her I was there for her, but her emotions were causing strain to our relationship. I decided she was worth the trouble because I loved her and I didn't want to hurt her further. She made me feel as if I belonged. So about a month after that (1 month ago) in which she was continuously losing her temper consistently she was forced to move out due to problems living together. She moved in with a close female friend of mine, who has since become very close to girl A. We'll call her roommate Girl B. At first I was glad to have more space, as I thought it would calm down the tension caused from our fights but soon her behavior became worse. She'd threaten to do hard drugs, or threaten to break up with me over things that to me often seemed unnecessary. But I stayed, hoping we could work things out. I've always been there to let her talk through things, and I always stop what I'm doing to make her top priority but it seems as if it isn't good enough or she doesn't value my effort at times. When I get close to crumbling she'll apologize multiple times and tell me she loves me and things usually go back to normal. So about a week ago something extremely dramatic happened. She went to hang out with her other friend, and this friend was talking to her ex who was saying he was missing and still loved her. So her friend ended up bringing girl A's ex without telling her and they ended up hanging out. I was out doing errands that day but promised and looked forward to hanging out with her. When I called her up telling her I'd be coming, she told me to forget it because she was job hunting and in the middle of something. So as I was walking home I had to pass by her place and she was out having a smoke. She saw me and ran over before I went in to say hey, and that's when she told me about him. So I tried to be understanding and trusted her while she promised nothing would happen between the two of them. I went off to my place, feeling afraid until eventually she called me saying her ex kissed her. Obviously I was crushed, and I was very off for the next few days emotionally but we got through it with her promising she wouldn't speak to him again or have any contact with him. So we got through things, with her still being very emotional as she naturally was at this point. It got to the point where I warned her that if she didn't begin to treat me with respect I'd have no option but to leave her. It wasn't what I wanted, but it felt as if it was my only option at this point. After that she begged for forgiveness and told me she'd try to change. She cried, and begged for a day, trying to get me to keep her as my girlfriend. I told her that we'd talk about it the next day as she worried and begged more for me to stay. So the next day comes, eventually we go and talk and then she sits down with me. I tell her I'd love to stay with her but I want her to put the effort into our relationship and attempt to not become so angry. I told her I understand if she can't always help it, but let her know it was effecting my emotions and well-being. Then out of nowhere she broke up with me. After a day of begging me to stay, she left me. She said she was too much stress for me, or that she felt trapped, or we weren't right for eachother. I decided maybe it was for the best considering recent events and went home crushed. I took a nap, and woke up with girl B (My best friend and her roommate) telling me that girl A was with the guy from before. I got extremely angry and confronted girl A about it through text. I swore at her, she swore at me but by the end of the night she ended up calling him. Girl B let me know all the things girl A did and said. She told me that she said the kiss with that guy was magical, and that after we broke up she went and cuddled with him. She told me that Girl A asked the guy to move in with her. At this point I was far past hurt, but kept texting my ex about this issue. After a day with that guy (With girl B having sights on them for the most part) girl A began to apologize over and over and over again, telling me she was sorry and screwed up, and that she'd never speak to him again after telling him off. I asked to see her texts and she allowed me, promising she didn't delete anything. There were no messages from the guy, yet when she told me to check her messages on facebook (Because she was still so sorry for hurting me) she asked him to text her and he agreed. After extreme amounts of fighting and depression I took her back a few days ago, warning her she's on thin ice. I told her I was emotionally drained, and that our relationship was causing me a lot of grief and depression. We hung out today and she had a breakdown crying on the floor, telling me she hated herself and doesn't want to lose me and that she'd do anything to keep us going. I suggested her going and getting checked out for her emotional issues and finding a way to help, but she keeps saying she doesn't have a ride and neither of us drive. She told me she wants to die and if I leave her she'll hate herself more and blame it on herself and can't promise me she won't do anything stupid. Since her and I got back together, kissing her, telling her I love her, cuddling her, talking to her, it all just feels forced and not right. I know she's sorry, but emotionally I've been damaged and I need time to heal but there's so much more going on. I've kept strong for the entirety of our relationship but I'm not able to do it anymore, yet I don't want her to hurt herself or go into a deep deep depression in which she blames herself. I understand it may be her condition, but she's taking me down with her. We're hanging out tomorrow to see if things go well but I made it very clear if she hurts me or keeps bringing me down I won't be able to handle it anymore.
So that's the first part. The second part involves girl B. Essentially her and I had a small two week relationship a month before girl A and I which had to end due to wanting different things at the time. I was sad about it, very much so, but we decided to remain friends and it's proven to be a very lasting and trusting friendship. So when girl A broke up with me, girl B was also just recovering from a breakup. I hung out with her one day before work to talk about our issues and she told me she loves me and regrets ever losing me. She told me she messed up big time and hates seeing the way girl A treats me. (Also, just for the record I know the things she told me about girl A weren't lies for personal gain as girl A has confessed) The hard part is that I actually consider girl B as a romantic option in terms of my happiness and I'm sure she suspects this but I can't get out of this relationship with Girl A. I realize it has to do with a tremendous lack of self respect but I'm so lost. When girl A and I kiss and girl B sees she loses it. She's becoming so hurt and I want to do all I can for her, but if I just refuse to kiss girl A then it causes a falling out in which Girl A, this girl I have a huge amount of memories with, begins to become even more depressed and hate herself further. I know it may be a jerk move being torn between two women, but girl B respects me, gives me freedom, I can be myself with her and she can be herself. She's there for me and actually knows what to tell me when I have issues. When I talk to girl A she says she doesn't know what to say. I'm not cheating on anyone, but it feels like it, yet I would never go as far as actually doing so. But when I show girl A affection (Which again feels forced, yet it's such a change to stop and I don't want to devastate her) girl B is on the brink of self harm. On top of that girl A is getting depressed because I can't show her my messages with girl B since it would cause a falling out between roommates and friends. It would only cause more hate and anger and I made a promise. I haven't been flirting with girl B or anything, but I'm trying to avoid what could possibly hurt the three of us further. I keep telling girl A its family issues, yet I feel like such a horrible person lying to her.

So like, what do I do? I'm so lost...


tl;dr: Im in a committed relationship with a depressed woman who hurt me and went behind my back while her roommate who's a lot more understanding and respectful said she loves me but I feel confused about every option.