Boyfriend and ex problems help please

Megan
I've noticed my boyfriend and his ex ( my ex Bestfriend ) have started talking again... I asked him and he gets totally defensive and he did tell me he'd stop talking to her but I know he won't bc he told her he would stop talking to me .. Which clearly didn't happen. I've known her for a loong time and she is kind of slutty and will give a guy whatever he asks for ... Me on the other hand has trouble sending my own boyfriend pictures.. He doesn't get the pictures from me so I have a feeling he goes to her.. I don't know what to do anymore I've seen all the messages He's sent her and I'm sorry but those kinds off feelings don't just crawl out of ur ass and leave... They just dont...