Should I believe my boyfriend

My boyfriend went out recently and said a girl kept chatting to him he was just being polite talking back to her and she was becoming very inappropriate, baring in mind she is married with 2 kids. He decided to leave and come home to me as we have been having some troubles lately and he didn't want to put himself in a position where it would jeopardise what we have if someone got the wrong impression. As he was leaving she grabbed hold of him and kissed him several times. He said he didn't want to physically shove her off as he is 6"3 and didn't want to come across as aggressive so he had to gently get away from her. As soon as he left he rang me and told me what happened but a part of me doesn't believe him... I just don't know what to think of the situation. We've had quite a rocky relationship he's told a LOT of lies in the past and this time around we were supposed to be starting a fresh and gaining trust again but then this happens.. Do I believe him or his is he just being his old lying self?