If i was verbally abusive to my ex can i change and how?

I was with this girl on and off for a few years. She was my first love( I was her 8th or so serious relationship) and she took my virginity (i was her 1000th probaly not lying here) During one of our big breaks she slept around alot and was very happy to bragg about this which i over heard. I also saw her with a few others and she controled them in variuos ways. Not defending myself just setting the groundwork here. So during our last year together when we got into an intense argument I'd get mad and call her a or disgusting and things of that nature. Rarely showed her much love and got very jealous & controlling when she would hang out with other guys. Afterwards i always felt like **** but would rarely apologize. I never wanted to say those things but could not control myself when out arguments got out of hand. I was never physical even though she hit me a few times, i never hit back. All verbal. She left me and this time its serious even though were still friends and talk like everyday. I dont ever want to do that again because I really did love her and losing her for real this time has hurt more than anything. Ive been reading books by john grey on how to treat your loved ones better and yourself. So all in all am i able to change? I never want to put someone else or myself through that again. And is wanting to change and reading self help books enough or would therapy be better?