The past should be the past, right???

The past should be the past, true. But in general you need to have an accurate, honest account of your partners' past to make an informed judgment about whether you want to be with her. You should want the same understanding about his past too, btw.

Meaning, once he knows about whether you once cheated, or five times cheated, or have herpes, or really need group sex to be satisfied, or whether you're a recovering crack addict, or whether you have this OTHER unmentioned baby living with her daddy in Florida, whether you have been convicted of child abuse, or whatever you have to bring to the table. Only then will he have the info he needs to decide to have a relationship with you.

If you keep such stuff from him, you're just building your house on a foundation of deception. He'll find out sooner or later and later is worse.

Whatever your little skeletons are, just own up to them. If he's okay with them, good for you! From that point on, HE'S obligated to keep the past in the past. HE'S not allowed to hold them against you if he's "okay" with them. If he's not okay with what you've done, well, its better for both of you to know now and end the relationship.

And cheating once in the past IS forgivable, if you show him how much you learned and changed and regret it. But likewise avoiding proven cheaters IS also forgivable, because maybe he's been cheated on one too many times and only wants to spend his energy on people who would NEVER cheat. He's allowed to want that, you know.

Be honest.

If you're truly not going to go down that path again, tell him so. Then if he starts whining tell him to watch Chasing Amy and STFU.

Past certainly reflects on what you are made of, but the important thing is to have learned from it... If you have, then you should also be able to explain him how you have and why you wouldn't do such a thing again... One thing in confrontations like this is that you should give him a space and see how he reacts... After all, you made your case and he chooses to believe it or not...

The way to let go of the past is to forget about it. He shouldn't be mad unless you cheated on HIM!

I agree with homer that you need to explain why you'd never do such a thing again. Then rent "Catch and Release". Jennifer Garner is all over her fiance's best friend after he dies but it's tasteful. Point being, the circumstance in which it happened makes all the difference.

The past does reflect on who you are so I understand why he'd be pretty upset. But he may come around if you explain the situation and how you learned from it.