Whats happening

So ... i have a girlfriend and we fight a lot because she contiues to talk to people that like her or she use to date and i get mad or jealous and she gets mad about it. Today she had these hickeys on her neck and i didnt say anything because i didnt want to accuse her of anything but she told my best friend they were real so i said something about them to her n she said it was a ' prank ' on her mother and the make up just wouldnt come off. I didnt know how to believe her. So we argued for a little and we made up and she said she would stop hurting me and everything would stop but im still hurt and idk why .... my heart aces and my head is spinning.