He hit on his female friend when he had a girlfriend?

Unless he has done something very recently, or has done something to you that would make me not trust him, I would. The past is the past. Especially for something that happened five years ago. People make mistakes and forgiveness is key.

Five years can be a chance for a lot of maturing if the guy was young. It also depends on how seriously he was dating the girlfriend - some girls think a relationship is serious when the guy is not certain it is yet! I think it is a little early to be labeling him as a cheater unless he was in his mid-to-late twenties when this "hit" occurred. If he was a teen or early twenties when it happened, he might have learned something in the meantime or be more serious about his relationships now. Now if he had just come to you from a relationship that broke up because he was cheating I would advise that you dump him, But it's too soon to say right now - and it was a girlfriend, not a wife...unless he was living with the girlfriend at the time, which would be like cheating on a wife.

Five years is a long time. Therefore you certainly cannot hold something that he did way in the past. Is he anything like this person now? That the huge determining factor here.

Just so you know...guys that flirt and hit on other women while involved with others are highly insecure. Quite possibly he only needed some growing up to do.

wow.... now, i'm guessing you mean that he flirted with another girl when he was in a realtionship... Now, the question was how serious was the flirting? because I know some guys just "naturally" flirt and some girls taking it as they want to "get inside my pants" when he's just saying hi, how's the day going... and considering this was five years ago... someone CAN (and I stress can and not has) change if he was a little bit on the straying side at one point of his life...

So, I wouldn't be worried... and more confused why a mutual friend would tell you about this when it happened five years ago unless she's jelous.... (which I have happen to me several times)...

i will consider him as a sick selfish pig who doesn't have any respect for women at all.