Boyfriends

I have had a few arguments with my boyfriend about a girl, there have been various rumors about them cheating and I have believed him that he is not. I am just so angry that he continues to have her as a best friend on Snapchat I don’t know if I am freaking out or if this is something to be worried about I talked to her and she claimed she would never do that to me and that this has happened to her way to many times for her to do it to someone else. She is one of the whores of the school. I have trusted him and I continue to because relationships are built on trust but am I stupid too? Am I being ignorant? He would rather work than do anything else and most of the time I have to make plans around him but I love him. I honestly don’t know what to do.