girl chose another guy over me?

my first semester at a university... this one girl was knocking on my door every week of the semester, asking if i would hang out with her.. she was obviously interested. me being the introvert i am kept my interest at bay. one night i saw this guy who she was friends with tickling her, while we were watching our favorite show, i found out later she slept with him, she then started being far from me and pretty much ditched me for this guy..... i t's a year later, they broke up like 4 months ago, i just found out from my room mate who went to her place for a gathering tonight, ( they are all drunk obviously, but anyhow he is telling me how she is opening up completely to him about me she told him she has a threesome with my room mate last year who i completed hate... she also says how she wish she went with me instead of ____ and that i'm a genuine, honest, good guy.... damn it all thought i hate that he told me that because i still have feelings for her and i don't want to have these feelings, how can i ever except being her 2nd choice?everyone i know will see it as me being her fall back guy. HOW can i accept that? should i not? Should i leave her alone? After what my room amte texted me i know i could easily get with her right now but a part of me is like..... am i that pathetic? do i want to be that fall back guy?