Is AUTHOR wrong in the post ? POST : 
(First of all forgive me for my bad grammar, English is not my first language)
things started a few months ago, my boyfriend's ex-girlfriend sent me a message to tell me that my boyfriend had been unfaithful to me, that they had kissed and she felt very bad about it, at first I hesitate but knowing that he had cheated on me once, it is when I take it seriously (He told me what he did immediately, we cut for a while but a few months later we went out again), then she told me that he told her the things we did in bed, things that I liked that they were impossible to know unless one of us told them; to add to all this a few days later a friend we have in common with his ex showed me some screenshots of conversations he had with some of my boyfriend's ex friends; generally they all said that he was not a very good person, that he had cheated on me several times, that he had never valued me and that he was not reliable. That's why I decided to confront him, at first he did not give much importance but when I notice that I was very upset about this he finally told me that none of that had happened and that it was just people with nothing better to do, looking to interfere in our relationship. We discussed a lot about this and although now we are better I don't know if I just let it go, I understand that someone may want to generate drama but there are so many people telling the same story.
To add, I know how he behaved in his previous relationships, he did some questionable things but we must consider that he was very immature since I have known him since we have 13.

AITA for not knowing if it is the best thing for me to trust him? I have to believe more in him? Or I have to bring up the subject again?