I hope you have accepted responsibility for some of your actions here. Nobody can make you do something you don't want to do. You have to have a little self respect and not allow yourself to be "bullied" into things even though I'm sure your self esteem and worth was at an all time low from the abuse. And I'm guessing you weren't honest with your abusive ex at the time of the break up when you wanted to be with the other, hence him following you after the relationship and mettling with the new affair. Maybe he's just insane and crazy, but he shouldn't have any say in that. What he did was pure selfishness and total disregard for your happiness. And that's not love. I've also guessing you stayed in the abusive relationship much longer than you wanted to, hence your attention to somebody else. All of these are important lessons you should grasp on and learn from your old relationship instead of just writing it off as "Oh he was abusive, it was all him." It takes two for a relationship to fall apart and you had a part too. Hopefully you want to fix those mistakes that were on you to make yourself better from that.
Anywho, old news, but you are going to hold to this new guy you fell in love with because I think you feel like it never got the chance to fully succeed or fail. You let somebody else break your relationship up for you and you are going to be filled with regret for that. What's done is done in the past and you can't change that. Try and forgive yourself for it. Your feelings are caught in limbo and you want to have what could of been yours before. I'm guessing you would like a long term and serious relationship with this person but you have to think logically about it: Would it work with the distance? Are you able to be patient and ease your way back in? Do you really want him in your life, or do you feel that you need him to kick your depression and be happy?
That's the thing. We all feel this need for somebody because we are in pain and we want them to take it away. You feel that he is the only one that can do that, hence it being 5 months and your feelings for him still are as strong as before. But you don't need him to be happy. What I think you should do is concentrate on yourself for a while and put in effort for yourself to be happy. Get yourself out of this rut, not depend on him to do that for you. Working out, hanging out with your friends, meeting new people, anything, everything you can think of that you enjoy. You need to be happy with yourself before you can really be happy with another person.
I think your depression and your guilt is tempting you to run at him with apologies and hope that the spark is still there. You could do that, and it could work, but I would advise against it. Too many times do we run to our exes with apologies and they give in because of their emotional mixed feelings and how they feel bad for the other person to see them in so much pain. It usually doesn't work but that's because we are taking them back for the wrong reasons: guilt is not what a relationship is based on. Not to mention he might not find that attractive anyway, neediness is never good.
I think you also feel like the clock is ticking, that all this time he could be finding somebody else, but as you remember, you don't need him to be happy. Work on you, make yourself that happy, confident girl from before and if you still feel that way when you are ready, approach him and take it from there. Whatever happens will happen and there is no use stressing about the "what ifs."
Waking up next to a beautiful girl,
Step outside and say hello to my beautiful world.