"However, I know someone who was in exactly this position, and trying to talk reason to her was like trying to talk to a brick wall...."
I have to laugh because he's being kind and not naming me here, unless he's put up with this from more than one person in his life, in which case poor Darling.
The irony is that the relationship really was on the rocks and I didn't know it, but I found out from his wife that he was really not so great after all. And I did learn, big time, to stay far away from closed monogamous types. There are happier hunting grounds to be found. Your case with your current love interest is different in that she has said "maybe", not "no".
And, um, isn't your former professor. Who is married with children. Married to someone who is in your circle of acquaintances. And isn't getting a messy divorce. I was an IDIOT.
He was so obviously not interested in a) poly and b) me. I mistook kindness for more because he ticked a lot of my "perfect guy" boxes. In retrospect, the major box I forgot to tick was "returns my affection". Oops. These days, if I have lingering feelings for someone who is that wrong for me, I process it through lots of talking and lots of writing. I may be able to get a whole book out of a dynamic I experienced when I was younger and very much desperate to be loved. Heavily fictionalised! If you go the fiction route, dear God change the details.
There's nothing wrong with expressing interest. Heartache happens when you do that after you've invested major emotion in the outcome. Me, I got hurt enough times that I made myself change for my own sake. If it is still worth your while to go on as you have, nothing anyone can say will change you. You have to figure out what you can handle and go forward accordingly.