I have strong feelings for a close friend, but am seeing someone

I (21yo M) have known my friend (20yo F) for about two years, and i've been going out with my current GF (19yo F) for about 5 months now. I've been the only person in my class to ask my friend to come out with the rest of us consistently, the others dont' seem to care that much. Although I love my GF very much, I can't help but feel strong feelings towards my friend. We've grown very close over the last 9 months, and I wasn't sure she liked me so I dismissed the feelings I had for her and looked elsewhere.. I feel love for my friend, but I'm not sure wether it is just a very strong friendship or our friendship turning into something more. Which is it? and that am I meant to do about it?

TL;DR - Strong feelings for best friend, almost stronger than feeling for GF. What do I do?