bisexual not yet i guess...
She's not wearing a ring, and it's not really clear whether she had Tanaka because of a wild night, or because of consensual sex.  Sooo i can understand the lack of that tag.  It makes the story better without it for now, anyway.
Surprised there's actually a sequel.  This author tends to like to make oneshots that leave us off at a point where we can see the most likely-case future, which is kinda where this one is.  Not that I'm complainin'