I (20F) can’t stop thinking about what my bf recently told me about his past (19M)

My boyfriend used to treat women horribly and did some awful things before we were knew each other. Including but not limited to emotional abuse, cheating, alcoholism, etc… He expressed his past long before we were together and I stayed because he has truly changed. He has never raised his voice at me and we haven’t gotten into any petty arguments. His past has shaped him into a better person and he never wants to be that person again. I don’t want to go into detail but I know for certain he’s changed, I can see it in his actions and the way he treats me.

However… I recently found out something new about that time in his life, that he was romantically involved with a 15 year old girl at 18. He shows astronomical amounts of regret but it just leaves a sour taste in my mouth, along with all the other things of course.

All the terrible things he’s done go against everything I stand for and I wouldn’t be with him if he hadn’t changed completely. Finding out the 15 year old thing really irked me though. Once again I got over the other things because he’s changed and tried to make amends with the women he’s hurt. If you found out your significant other had a horrible past would you break up with them?