I have a huge problem and i honestly dont know what i should do

So i have this problem right, i know this girl, let's call her Sarah for a second that's easier. So i know Sarah for about a month now and we're really close. Sarah has a boyfriend but has feelings for me and i have feelings for her. I've kissed her and even fingered her.. See the problem is she doesn't want to hurt her boyfriend's feelings and that's why they haven't broken up yet. I can't meet up with her when he's there cause then he will get mad, which is understandable. See my problem here is, this has been going on for 2 weeks now and i don't really know what to do with this all. I really like this girl and i would like to start a relationship with her but as of right now it's not seeming like anything is going to change. The boyfriend is over there right now for her birthday, which i can't even celebrate with her because of him like wtf?, and i'm getting pretty impatient..

I hope somebody can give me some advice on this. Should i wait and keep loving her, or just let it slip and wait for my next crush to like me back...

Greetings, ImA15YOBoy.