Most Helpful Girl
Respect yourself and tell that girl to eat shit and fuck off. That is totally inappropriate: "OH hey I fucked another guy but I want us to be 'close friends" (aka in case shit goes wrong I want you as a fallback tehe) so you're okay with that because you're a total pushover right?"
Please, do not do that to yourself. You deserve more than that.
Most Helpful Guy
I wouldn't talk to her until you've had a chance to deal with the bitterness of having her cheat on you.
It's a compliment that she still wants to be friends. I know that sounds strange, but it's still true. Consider it when your head is cooler, and you've taken the bullets out of your gun.