Should I believe them?

So, my partner and I have been together two years. When we first got together he wasn’t over his ex who had broken his heart, note he never lead me on, we were friends but had an incredible connection. Once he was fully over it, we eventually got together and things, most of the time, are great. He is helpful, loving, and great with my two daughters. He is affectionate with me even though he hasn’t been with women previously. He lost both parents and struggles, at times, with affection. But with me, he grows daily.

However, both of his exes, the one who left him and the one he was with before her who he has a son with, have told me he can be awful, cold, and can be cruel and heartless. One told me he made her get an abortion. The other told me he is emotionless and cold and she spent seven years living miserably. Firstly, he has told me in the past he wasn’t a good partner, that he could be all of those things and was indeed cold and mean to his partners, however told me after his heart got broken he pulled his head in and didn’t want to be that man anymore, he realised he would end up very alone if he didn’t change. He loves me hugely, I’m not blind, I can see it, hell even his lifelong friends make comments. He does everything for me. From when I first met him to now I can see the change in him. He gets better, not worse, and adores me.

But

BUT...

On about three or four occasions in our two years I have seen the ugly side to him. Always during a fight. He can say cruel things (name calling etc), be nasty and once even pushed me. It bothers me as I can see what they’re saying, I can see that side they told me about. I confronted him, and told him I won’t be treated like that, and the night he pushed me I even got in my car and left. I made it very clear I will not tolerate it. I WILL leave. He told me he doesn’t want that side to come out and won’t let it happen again. That I’m the best thing to happen to him and he loves me in a way he has never loved someone before. And since then, I haven’t seen that side to him. That was about 6 months ago.

But I just always carry around this nagging feeling over time it just might raise it’s ugly head again, like when we get more comfortable etc.

So, do I believe a person can honestly change? I mean his heartbreak three years ago really did change something in him, it was the first time he’d ever been hurt and his ex dragged him through the mud so I am sure it did make him think about himself, I spent six months by his side as his friend watching him recover before we became an item another six months later, so I know it affected how he thought, and when he committed to me he, as I said, is mostly incredible - I can’t fault him as a partner. I’ve never been adored the way he adores me. But I have seen the ugly side. And it has bothered me. And I do get scared it will appear in the future.

Advice?