I don't think anything excuses cheating. Along with lying, it's one of the most utter forms of disrespect. I mean, you're giving your partner your heart, your body, your trust, your soul, and they go and betray all of that by jumping in someone else's bed.
Now whilst cheating can't always be put down to dissatisfaction, its inexcusable and unforgivable. If your partner thought it okay to go and sleep with someone else, honestly - what is there to talk about or resolve?
I'm big on loyalty. And even if you're young and going out with someone, you still make a commitment, however small. If you wanna run around and be free and have sex with loads of people, then do it - I mean, we're all young here. But, if that's the person's attitude, then DON'T commit yourself to someone who may have a very different opinion on things.
If you only take up the opportunity because you think it'll never happen again, that is just plain selfish. Its horrible to regret what you didn't do, but not when you were looking out for someone elses feelings.
If you're young, it's totally natural to want to get around and see what's out there. So, if you wanna run around like that. STAY SINGLE. I say and will always say: cheating is inexcusable and unforgivable, and if my boy did that to me, he'd be out the door and I wouldn't want to hear another thing about it - ever.
By the way, boyfriends have cheated on me in the past, so I'm not pulling my opinion solely from belief, but experience as well. To this day I have never cheated on a boyfriend and hey, let's say I hope I never will.