Guess my issues are.... I have never went from being friends with a girl to fucking her... How will it change our friendship, what are the limits? Plus, how do I handle being the other guy.... Know just so everyone knows I don't want to be the other guy forever, sooner or later she is going have to make a choice, but for now I am just trying to go with the flow
friendship = ruined, but who cares, you've been trying to get in her pants since the reagan administration and she has a boyfriend, what do you expect?
you handle being the other guy by shutting the hell up, no seriously, when a criminal does a crime, how do they get caught when they first get away? they will literally snitch on themselves .. with that being said, don't go around telling everyone that your banging "that dude's" girlfriend, don't write all over her facebook, and only hang out with her in places where people can't see you.. act like you been there before or else it will blow your cover
and you may want a relationship, but i doubt that will happen (i also doubted she would give you anything other than blue balls but i guess i was wrong about that)
even if she did want a relationship, why would you ever want to be in one with a girl like her? lets say she dumps the BF for you, she will get bored with you, and find another other man .. you're sharing her now, expect to share her for as long as you know her .. honestly the main (if not only) reason she has you on the side is for attention and now that you said all the right things to get in bed with her, she will only be with you as long as she is with her BF because the biggest appeal about you right now is that you are bad, forbidden, naughty .. she gets the same rush every time she hooks up with you as you did when you snuck out of your parents house late at night as a kid and didn't get caught .. this will probably not last long unless you pull some cliche, romantic comedy stunt
good luck