Spent 18 hours non-stop with her yesterday and I took the advice of many of the people I've discussed the situation with: bringing up the fact that she's cheating on her boyfriend to do things with me. I also brought up the double doozy with it: if we were to be in a relationship, how would I know she wouldn't do the same thing to me?
It honestly had kinda been bothering me and I was hoping she'd have a good answer for me. She didn't, and was actually quite distressed about the fact that I felt that way and fully understood why I'd be doubting her. That particular discussion lasted for about an hour as we evaluated our entire current relationship, previous things that'd happened, how she feels about every guy that I've known she's been with (including her boyfriend, for which she apparently has almost no romantic feelings for anymore considering he's whiny, antisocial with her friends, has repeatedly cheated on her, and is constantly gone miles away for work), and even now it's feeling kinda promising. She also told me that she's really not in much of an actual relationship at the moment while she's been living in the same house as her boyfriend. Nothing really happens with them and they are just at an awkward stalemate. They aren't even so-called "Facebook official" anymore.
Obviously I'd be taking a bit of a trust leap if we decide to go through with it. I set my boundaries saying we couldn't be "official" until she's actually broken up with her boyfriend, which may be anytime now.
Out of curiosity, I did ask her what her boyfriend knows/thinks about me. She apparently talks about me all the time with everyone she knows and it pisses him off because he hears my name so much.
[Very nsfw stuff in this slot]
We both let out a lot of gooey no-chill confessions about how we really feel about each other. That was an extremely adorable experience that had me smiling the whole time.
So I guess things are looking more in my favor at this point. The saga may be approaching a close.