Can't chose between 2 guys!?

im gong out with one of the guys:tyler-who has been my best friend for a year, boyfriend for 2 weeks. im not physically attracted to him, but with the other guy i like, aaron, whos a senior, i am extremely attracted to. i've liked aaron for 4 years, and we just now started talking and he likes me back, he doesn't know im going out with tyler. aaron calls me all the time and i ignore it or blow him off when he wants to hang out, i feel really bad, and im not sure which buy is right for me...