She has a boyfriend, I've known her about 6 months. She seemed interested despite that but there were social reasons I didn't want to proceed. I started seeing someone else.

I have to see her socially. She still likes my attention. I figured due to the non escalation by me I was acquaintance zoned.

She started dropping mention of her boyfriend a a few times. I didn't really respond, but didn't want to be that guy so I removed my attention from her. Ok with being civil, not ok being the guy she talks about her boyfriend to.

The following time I saw her, she mentioned her boyfriend but she felt she kind of had to or else she couldn't describe what she was talking about. But she reacted very oddly to this, the second she did it she got this very unhappy look on her face and looked down, then started glancing at me back and forward with the unhappy look. I withdrew.

I saw her out in public by chance with the boyfriend. I'd never seen him before. When I see her, she gives me this unusual glare.

The next time I saw her following this she is being super awkward initially. She looks pissed off at me. Keeps giving me glances. There are 6 of us out to dinner, so I go and make conversation with her and then she lightens right up.

What am I missing here? I thought I was friend zoned to oblivion. Why these emotional swings.