Broken promise..

Okay so my boyfriend and I take promises very serious. If we promise it's like us putting our life on the line. And We both promised we wouldn't talk to certain people (for reasonable reasons) and well he broke the fucking promise and I accidentally went on his Facebook (he was logged in on my phone and thought it was mine. Saw a message from the chick thought it was to me) and he's having a fucking convo with her. Btw she goes to every single footy match and training he has! And flirts with him and talks about him 24/7 wtf do I do!? I can't say I was on his Facebook...