Originally Posted by
BackUpOrGetStng
Break it off with her and go no contact. Tell her to get in touch with you if she decides you're the one she really wants to be with. She'll probably come crawling back within a couple days. If not, you still have your dignity and you'll already have begun healing.
I would skip the part where you tell her that you will be her backup plan. Break it off, go no contact, and move on. If (when) she decides to contact you later, decide then how you feel about it.
Good decisions come from experience. Experience comes from bad decisions.