I'm cought in the middle of two beautiful wemon idk who to choose my gf org friend tht I like...?

Ok so I have a gf and I've been talking to this other girl ive known for a year and she has a bf but I told her I liked her tonight cuz I was with her amd we were all flirty and stuff and she said she likes me and I told her tht I'm not the kinda guy that will cheat on ur gf it's just wrong! So I told her in the future when we r both single tht we can date she agreed but my bestfriend had hooked up with her I guess Thts what he calls it (they just made out and stuff so Idt it's hooking up and she was single when she hooked up with my friend she didn't cheat on her bf just making tht clear :p ) but idk how to tell him I like her I didnt mean to fall for her it just happened and I feel horrible because I have a gf but at the same time I feel great cause I told her I liked her... And she likes me too but we both r in a relationship we promised we'ed keep the attraction to eachother between us cause we don't need ppl knowing but still I was looking at her profile pic on fb and she's so beautiful and pretty I wanna date her now!!!! It's just we're both in a relationship and my bestfriend had a thing with her... Idk what the f�ck to do!!