Argh! They always have to be bi!
What's wrong with that? Ladies loving ladies are all cool in my book xD Plus it's not confirm that she's bi, she could be pan or smthing ¯\ _ (ツ)_/¯
I think it was meant for the ladies loving men thing, not the ladies loving ladies :P Also how is she not bi since she currently has a boyfriend (or more in the past)?
Tons of girls dated men before they came out as lesbian (also applied to guys). It only matters in how she defines herself (which we don't know yet or probably never will?)
And like many have said, I don't think there's any reason for OP to be mad at Emi for having a sort-of bf since she's clearly into the badass Kei (even her name is cool af). If this continues to be well-written then the boyfriend-but-not-really shouldn't be a problem.