I would say MAYBE she went back to the church--but didn't OP say she's withholding all intimacy, including regular physical touch? If you can't track where this is coming from then she's cheating man. Women are weird, they can't have their hearts in two places. Even if she hasn't yet fukked someone, she could just stop having sex because her heart is guilty about the OTHER dude.
Honestly it doesn't matter if she's cheating or wants marriage. Bottom line is you both don't want the same things, anymore. It hurts, I know, we've all been through it, but this is part of living, part of being a complete human being. Everything happens for a reason. When you find the strength, let her go. The time will come when you're ready. I don't necessarily think you have to rush things, as I think breakups go through stages, but you must know that it will get worse and your heart will gradually ache more until it breaks.
Good luck.