Having been in a similar situation... we were dating throughout college, college was ending, and I was freaking, knowing that if we stayed together at this point, it was pretty much a red carpet walk to marriage, and I wasn't sure if I was ready for all of that. He was, but wasn't... he was on the fence. But we spent our time similarly - together, calling, mushy, etc. Much like now, actually.
So if this is a similar situation to ours, and it sounds like it is... I think that if she's not getting it on, she's considering it.
What should you do? Take the long view. Seriously. Do you love her? If so...
Go to the wedding. Next time you talk for more than 2 minutes, bring it up, admit to being a dolt, and tell her you'll go.
Give her all that space. Be happy to hear from her, loving, but let her call you. DO NOT PRESSURE HER, DO NOT GIVE LIMITS OR ULTIMATUMS. Pressure will just make her run. As stereotypical as it is... women (okay, and men too) often want what they want until they get it. Quadro gave me space, and I didn't like it. I wanted him back. I wanted to call him and tell him what happened that day, or ask what he thought... I missed him. Basically, it's like that bad insult joke... Go away so she can miss you. But make sure she knows you love her. Keep communicating.
And if she does cheat, and she tells you in the "cleaning the slate so we can move on together sort of way"... please, don't write her off. This is one of the most emotional, scary, pressure-filled times of your/her whole life. There is a LOT of shit going on. A mistake in judgement now does not mean anything about how she'll treat the rest of your lives together. The experience may even illustrate more clearly to her why you're so wonderful. Trust me.
If it matters, I too was a budding actress getting out of school. And remember also that 22 is younger than you think. There are still a lot of lessons to be learned.
Good luck, keep us updated.