Boyfriend lied

A few days ago my boyfriend lied to me for the first time. Some girl added him at 1 in the morning I asked him who she was he said that it was some girl that he went to school with and that nothing happened. But when he told me that I could feel his anxiety after that and then I remembered that he told me about a girl that he was with she had a boyfriend at the time but it wasn't a good relationship so he was trying to convince her to break up with her boyfriend but while he was doing that he was also sleeping with her. So I'm not really sure how to handle the situation. We had an argument about it yesterday and I called him a hypocrite because he preachers on honesty and loyalty but he lies to me about something that he was honest to me about the first time when he barely knew me in about the Loyalty this girl had a boyfriend and he was sleeping with her at the same time. He gets upset wouldn't girls cheat on him but it's okay when he sleeping with a girl with a boyfriend. I need advice!