Hey there AlleeCat I didn't quite get through this entire thread, but I'd like to address your original question a bit.
It's tough when you are gay, you can't really know if someone else is gay. Hell, sometimes when you are young people don't even know if they are gay yet. It can take time.
So us old people are at an advantage. I can spot a straight dude in the dark, in the fog, across the street. Still, now at 36, it can be difficult to spot a gay man. Luckily gay dudes sorta advertise a bit, but not all, some are scared. It's a tough thing.
With girls it's even more rough, especially while young. Straight girls will occasionally, while young, have sex with other girls. This happened in college all the time. Every other girl was 'bi' or whatever. It has to be horrific for a lesbian. It's just so hard to know who is who and what is what. Up is down, right is left, do I take the blue pill or the red pill gggaaaaahhhH!!!!!!!
You do have a huge advantage though. You can straight ask this girl, "Do you date girls or boys?" You can do that and not risk much blow back. Oh sure, if you get all creepy and nervous about it then you might have some blow back. But seriously, if you went to lunch and you asked her if she is dating anyone, and she gives an answer, then you'll know, but if she says she's not you can ask, "Well, do you date girls or boys?"
Easy.
As a man if you fuck that conversation up things can get pretty bad. Men are subject to assault and even murder. For guys I advise they don't ask anyone they aren't sure about. Stick to gay bars and interweb dating boys, much safer.