How long do i wait before getting with her again?

My first college semester this one girl and i had a lot of stuff in common and she would come knocking on my door every few days whenever something was going on , asking if i wanted to hang. one day she had sex with this one guy at our dorms who was pretty aggressive at getting with her, i'm more laid back and i thought something might be up when we were all in someones room and he started tickling her. They got into a relationship eventually but before that i told her how i felt and she, was like " we are not dating" and was like i could really fall for you. She just got out of a relationship of 3 years at this point and wasn't looking for another one so quickly she said. But i guess having sex with this other guy made her change her mind. Anyhow it's been a year, they broke up like 5 months ago. My friend who has been hanging out at where she is living tells me how she's telling him , i wish i would of went with____. He's such a genuine person, and she apparently is talking about me a lot to him. I liked her a lot and was hurt back then but after so long i've recovered. I know if i go with my friend to their next drinking night she will start flirting with me. My thing is though i don't like the thought of me being her 2nd choice, how long do i wait before i'm not considered the fall back guy? should i even give it a shot at all?> i kinda feel pathetic if i do in a way. but should i really turn down a chance that could turn into something great

- - - Updated - - -

also if you are wondering why i didn't have sex with her, it's because i'm a virgin and wont lose it unless i'm with a girl for a really long time