should i date my best friends boy friend?

Ok so i have this friend and we just mad up bout 3 months ago and she has this boyfriend and he is so funny and gorgeous and i think that im in love with him. but we were goin to church one time not to long ago (all 3 of us) and well at church she sat in between us and he put his arm around her and then rubed my arm with his fingers, so i looked over at him and he winked at me i felt breathless. <3 but i feel bad for my friend cause i havent told her because she will flip out on me and we will loose our friend ship but she cheats on him all the time. and i kinda think that i should date him cause shes done it to me before. i LOVE him but i dont want to loose her. i have other friends but nobody at my school likes me . i just dont know what to do iv been so stressed latley cause  of it and either way im unhappy and happy at the same time HELP ME!!!