This is just what I would do, so take it the way you want.
If my boyfriend cheated on me, I would break up with him, no second chances. However, as ticked off as I would be if I did find out, I would rather know, than stay in a relationship that in which I had been cheated on and never find out.
The thing is, your boyfriend deserves to know. It will undoubtably upset him but it his RIGHT to know, and then decide what to do about it.
And cheating on your boyfriend is an awful thing to do. It is probably the worst mistake in a relationship, and there is NO excuse for it. However, making this mistake does not make you a skank, or a bad person at all. It does make you human. Because like PDM said, all people make mistakes. Making these mistakes make you human. Just learn from mistakes.
