Dating

I just found out that my boyfriend left his ex because of me?

We haven't been dating long, but when we met we started off as just friends in a group. He never mentioned he has a girlfriend, nor did his friends. But I never asked either.
Then few weeks after hanging out with them, I developed a crush on him and we hooked up. He asked me to be a couple, I said yes and we've been dating ever since.
Yesterday we talked about exes for the first time. I am not really keen on talking about exes because I think there's no point, and maybe it's my fault I never initiated the topic. But he told that he was actually in a relationship when we met, and that he broke up after we hooked up.
Now, here's the worrying part: he said that nothing was wrong with her and their relationship, that he just liked me more. He felt we clicked and he wanted to be with me.
Then I asked him about past relationships and he said that that's usually what initiates the breakup, that he usually meets someone better. He has a history of leaving girls for other girls. What shocked me the most is the way he talked about it like it's the most normal thing in the world. He doesn't see anything wrong with it.
We had an argument about all that, I told him that then there's a high possibility that he will leave me too for someone else, and he said that yes there's always a possibility for that. I asked him how does he see a commitment then, and he said he is fully committed as long as it lasts, and that he always hopes it will last forever. He wants to be into only one girl forever, but it just didn't happen yet.
He is extremely immature, I see that now. Am I right to break up with him?
I just found out that my boyfriend left his ex because of me?
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