OP just reading your post, I found myself getting furious on your behalf.

End this, this is no way to live, you need to respect yourself more than this. This relationship is fundamentally unstable and will implode sooner or later, regardless, why would you want to be in a relationship where you cater to all her needs with no attention to yours?

You're her safety blanket, and it's time to roll that blanket up and return her to the streets where she belongs. The lack of respect displayed by her actions and dry humping a dude at your damn engagement party in front of all your friends should have been the straw that broke the camel's back, have some self respect dude, this ain't it.