How to stop thinking about your boyfriend's ex? Helpppp meee

I'm in love with my guy for a few months and we are having fun, he loves me and I love him. But, sometimes, I think that I'm too selfish because I ofter go to his social network and find some things about his ex girlfriend and how were they. I dont like me to do this but I cant help to stop doing this. Can you give me some advices for my prolem?????