So, there is this girl that I like for some time now. I know some of her female friends, so that's how I know she has a boyfriend. Now, I've been trying to get in touch with her somehow and see how how it goes and with a help from a friend I've managed to do it. We saw each other once with a friend and once afterwards we took coffee together. Always a pleasant talk, but nothing more happened. We texted casualy in the meantime, but nothing special. Now she invites me and the friend who introduced us for some drinks for her birthday.

In general, what are my options here? I really like her, but, obviously - she has a boyfriend. She never mentioned him to me, so I know it from her friends. Do I drop it, or escalate somehow, and if yes - how?