I think the exact opposite of what the last post says.

People do make mistakes. They make a lot more mistakes when they're young, but intelligent people learn and grow their whole lives and that means mistakes are made. People's mistakes are not what define them. What defines a person is what they learn from their mistakes.

I will say, however, that it is unlikely that you will "never be happy unless he's in [your] life." A lot of people feel like that about their relationships at 17 and most of the time it turns out not to be true.

In any case, if you want to give him another chance, I don't see any reason why you shouldn't. If he cheats on you again, you'll know where you stand. More than likely, you won't still be together in a couple years anyway.