OP here: As I said in my post, we are just friends, and she has a boyfriend, so there is no potential for us to date. There isn't, afaik, anything I've done to show that kind of interest in her. We're friends.
I should also mention that when we met, she put her number into my phone herself. I did not prompt or ask her for it. There is also the factor that she is in a place where she knows nobody since it's far from home, so if anything she's in a position to make and to keep friends.
Still, your post has not failed in making me feel shittier than I did before.