I don't understand why you wouldn't be able to start a new group.. Sure it would be difficult, and maybe you'd have to start over compleatly or/and re-write a bunch of your materials, but.. I'm sure there are a ton of people who'd love to come play with you. Just look around for it, there are a bunch of forums and facebook pages for people who are looking for this sort of shit. Fuck if you live in Manchester (UK) I'll drag meself over to your house and D&D the shit out of it.

Anyway, look.. You could, if you want start over, write new shit, and move on from these people. Or, you could invite them over and have a sit down with them. If you miss at least some of these people (the actual people, not for the sake of your worldbuilding, and them being a part of it etc.) tell them how much their actions hurt you, and that they're supposed to be your friends. Sexual assault is serious, and people often go into shock when they hear about it. It's a kind of "But what if he did" kind of feeling. I'm not saying that they acted in an OK way, because when a friend of mine was accused of it, I asked them fucking questions and realized that the girl in question was full of shit. I'm saying they don't react to/deal with shock very well. And some of them, I'm sure, are just immature and thoughtless.

If you really want to be able to forgive these people, I think you should tread carefully, and not do so before you make perfectly clear to them how their actions affected you, and that they hurt you. And honestly, I think you should vet them a bit. The people who were the worst (cos there's always some) you should cut out and replace, and you'll know who they were. Personally, I think you should start over. As I said, maybe you'll have to start over a bit, but it's not "impossible" to just find new friends who'll take over. Good luck.