What do you do when a boy cares too much about what his friends think?

This boy and I started having a thing and we'd hang out and have lots of fun together up until he just stopped talking to me one day. I found out from his younger sister who is my friend and her boyfriend that his guy friends were giving him **** about stuff i've done in the past. I'm an overly nice girl and I wear my heart on my sleeve so i've gotten myself into some pretty sticky situations. I don't want my past to define me. what do I do? I dont want to just give up cause I know that there's something there.