Need some advice

Well my boyfriend went out to dinner with his boys for one of theirs birthdays and went to Buffalo Wild Wings ... And I have his password to his facebook and I was just curious looking around and this pops up..  Didn't tell me he went to busters for apparently a "drink "  he doesn't know I creep on his stuff a lot but then randomly delete the convo between him and her .... He says she was a friend... But why delete the messages ? Acting like I wouldn't see ...  Remind you im pregnant 17 weeks!!