Can't seem to get it right. What's my problem?

Hey guys this is my first post here and I'm just hoping for some opinions/views from others.

I've been in a relationship for 12 years (we started dating when I was 15) and its been quite toxic for the most part. We obviously have great days but the bad days can be so bad I question how we have lasted this long. We've never been physical towards each other however he grew up in a very verbally abusive home and has carried that verbal abuse in to our relationship. He's very quick to anger when things don't go his way, he calls me every name in the book, puts me down and tries to control any aspect of my life he can. I don't even go out with friends because if I do he calls my phone 100x to see what I'm doing and if I don't answer he thinks I'm cheating so I avoid going out all together to avoid any arguments. It's like I'm constantly walking on egg shells not knowing what will set him off. Now when he's happy or not in these moods (which isn't very often) he's the most loving man and romantic and those are the moments that have made me stay so long. But those days are few and far between. I'm not a stupid woman and know I should not be with a man like this who is always trying to bring me down but every time I want to walk away I can't. I have a wonderful support system with family and people who love me and are willing to help. There has been no feeling of love between us for several years and we've broken up a few times over the years yet we keep holding on, I don't know if it's a habit because of how long we've been together or what it is but I know I need to walk away.

This is where things get complicated. About 7 years back we got introduced to a guy who became a great friend to both my boyfriend and myself. He was at our house or hanging out with us everyday and after 3 years of always being together me and that guy developed feelings. I was not pursuing anything or trying to be sneaky but once he told me how he felt I started seeing him in a different light and things got more out of hand then they should have. I've never been a girl who cheats or sleeps around and find it wrong on every level when you have agreed to commit to each other and I tried to justify it because my boyfriend has cheated on me several times however I know two wrongs don't make a right. Any how the friend and I ended up sleeping together a few times and ended up eventually falling in love. This guy didn't date anyone for 4 years just waiting and hoping I would one day make my way to him. He never pressured me or told me to leave only expressed his feelings and left the choice up to me. However recently he just got mad and stopped talking to me because he can't stand that I've stayed with a guy who treats me so horrible when I could be with him and be treated like gold. I know in my heart this guy is my soul mate and I feel absolutely empty inside not speaking with him anymore, it breaks my heart but still I'm here waisting my days away on a man who lies,cheats and treats me like garbage and I've now messed up things between me and my soul mate by holding on to something that is never going to change. Why can't I just leave ?? I'm throwing away my happiness out of guilt and I guess shame but it's eating me up inside.

I apologize for such a long post but I'm literally lost and I realize I should have ended things before ever jumping into things with this guy but I did and would appreciate anyone's advice. Thanks you

Unfortunately it sounds like he just wanted a fling and to see if he could get with his friends gf. If the other guy is so bad why don't you leave him?

a great friend to both my boyfriend and myself. I ended up sleeping together a few times. recently he just got mad and stopped talking to me.