So, background. About a week or two ago i was in my friends office, she works as a secretary for some special program we have on faculty. Anyways, she is friend with (well, most of all students) this HB9. So while i'm chatting with this friend HB9 comes in for some random questions. We introduced ourselves. I didn't intervene a lot in convo because it was mostly business, i just jumped in two times saying I can supervise the exame (because they had problems finding professors for that). The first time she did acnowledge me, second time i got longer eye contact and a smile. They finished with conversation, said goodbye to my friend while she was walking out of the office. like 2 seconds later i also said goodbye; she turned, looked at me, smiled and said goodbye (again).

This friday i went to this friend again, and HB9 came to her office again (just my luck). This time the interaction was longer, my friend even told her about out "work relationship" (shes kinda cute, so C&F and she returns it, married tho). Even got a few good negs with HB, like "Oh you give instructions for that class? I haven't done that exam yet(really didnt and she helped her friend with that subject). How much do you charge an hour? I mean for the instructions? " which got a good response.

After that a HB schoolmate (girl) friend came. They were going for the coffee and my friend said i should go also (I told her i think HB is cute). Something about me paying for the coffee like a gentleman, i said because of ratio 2:1 they should buy me coffee. And HB actually did end up paying for my coffee because i didnt have any change. She also complied really quick (Hey guys, looks like I'm really gonna have to ask you to pay for my coffee, i have no change. - Ok, I'll pay for it.)

She sits down next to me, her friend across the table. We talked for almost an hour, got a few good laughs. She hit me leg to leg two times but always said "Sorry". Once she insulted me unintentionaly ("When you do that exam, you really are a student of this faculty". And i don't have that exam) so i acted insulted (AAAAAww cmmon!) and she laughed and wanted to touch me on the shoulder but stopped like 10cm before reaching me.

They had to go and she said next time coffee is on me. To which i went "Yea sure, just call me(they dont have my number)". She said to just come around, since they are studying there all the time.
After that I went home and on 1km walk we crossed our paths with HB 2times lol, everytime got a smile.
Looking back, on the walk home i should probably go for the number; before the friend would be the problem.
And as I've been told, she is currently not in a relationship.

How would you proceed with this one? I know i cannot ask her out/for the number in front of her friend. And i also need some good reason to get her to hang out outside the faculty (we can get coffee there :/).
I'm thinking just another coffee for begining; if friend is not there then good, otherwise try more kino.

Any input is welcome.