Her attitude is confusing. “What’s there to say? What’s the big deal?” I don’t understand why she didn’t recognize that you were a potential romantic interest. You say she talked to you in a way that made you feel like maybe she felt something. Even if she liked you only as a friend, telling you about a boyfriend would be important to reveal. Either she is the most innocently naive person or she may have been leading you on.

Since she is causing you upset, I think I’d suggest too, to break from her. As they say, ‘there are plenty of fish in the sea’, so keep meeting new women until the right one comes along.