Dear Bitter Guy -- Relationship advice for singles and not-so-singles

Dear Mr Bitter Guy, I need dating advice ...

OK i have been on and off with my boyfriend for a year. during this time he lied and cheated and had other girls and slept around I was with other people in the times when he had another girlfriend. He cheated on his most recent girlfriend with me lets just say we were very rocky.. and its been nothing but drama for us. but just recently like 1 month we have gotten back together. and are officially together. and things were amazing until i messed up. He is overseas for a year. everyone at home tells me im dumb for waiting and everything well I had a one night stand. I know it will NEVER happen again and I know how he is and he will not forgive me. I regret it so much and have been crying for days. Should I tell him?

Or should i just let it go and see how things are when he gets home...? the thing is i worry a lot and i'm afraid its gonna come out later. he has lied to my face why can't I lie?
by the way he didn't tell me about his cheating. he was just dumb about it.