what should I say or do?????

Okay so yesterday I was going thru my boyfriends phone and he's texting an ex and asking her what time do she wakes up in the morning so I act as if I wasn't lurking in his phone but the text was one month ago or whatever! The girl is his sister bestfriend and he stay going over his sister house lately but he don't kno that I KNO bout the girl before we got serious I would look on Facebook And see them hugged up etc on his sister page also in his inbox they would be inboxing around last year when I didn't KNO him yet I guess she had a man and she would be sneaking with him to  pick her up at his sister house now that I'm with him a year later they are still texting and she also sent me a friend request not knowing that I already know who she is should I confront him about the situation I mean he doesn't know that I know he used to mess with her or even seen the inboxes what should I do