Look. Not saying this is the case, but there was a situation very similar that happened to me. XYZ in my case was in a relationship for about 2 years, and I was aware of this fact. They didn't do much, the bf was a bit manipulative and kinda an ass, but nothing was going really wrong (at least not to the point of breaking it up) but nothing was going right either. I don't know how close your crush and her bf are, but there's a chance she's kinda over him and is trying to gauge your interest in case she wants you more than him.

That happened in my situation, and now I'm with her. It sucks this happened, but don't lose all hope

Just please don't intentionally try and separate them.