Badly hurt. Him or have him in my life.

I have been hurt from a year. I was in a relationship with my boyfriend from 4 years. We broke up because we used to fight a lot n there was no understanding btw us. He is a very possessive person so it used to trouble me a lot. It's been 1 n half year since our break up but we are still in contact n we are close. But we still fight. He has become friend with a girl n it's been a month n I knew about it. When we were in a relationship we had never been in contact with girl or guy Because he didn't like it. He is open to me N never hides anything. But he lied to me that he doesn't txt her but she does. Recently I saw his phone n saw that he has been texting her in a very close manner which deeply hurted me. I'm very hurt from inside n just pretending to be happy from outside. From 2 months I can't explain u that how much I have been hurt. I feel like I'm slipping to depression. I need someone's help. I don't no what am I feeling n I'm not able to leave him or have him in my life.