Most Helpful Girl
Because she is a childish or maybe her boyfriend is tired of her and he wants kick her ass out and before it happening to her she wants be sure that you'll be there waiting for her.
Most Helpful Guy
She's crazy. Be glad you didn't stick your dick in it.
Seriously though: It sounds like you were the guy she was keeping around, either as a back-burner, backup option, or emotional support. She probably had no intention of every seriously dating you, and was keeping you around for whatever reason, while she found someone else she DID want to date.
Best thing you can do is just completely move on.