How tell a girl i am head over heels for her...its complicated!!?

ok..so since freshman year (im a junior) my really good friend (Nikki) has a best friend Taylor... i have known her since 9th grade but its been just this year that i have got really close with her (as friends). About September or so i got a mad crush on her and its not going away. We hang out everyday pretty much during and after school an she kinda shows a flirty side towards me (i think)...but here is the kicker since early feb she got a bf and he treats her like crap an she knows it too and when everyone asks her why they are together she doesn't have an answer. its seems like everyday they are fighting over something. They never do anything together, well they do hang out but not often. Whenever they go to lunch together she usually invites me to be the 3rd person if im not busy....She is going to prom with him and i was going with Nikki (as friends) but she has a rodeo that she cant miss so it didn't work so so Taylor insisted I come with her an her bf. I decided not to go b/c i think it would be really awkward just the 3 of us. I always plan out how i tell her how i feel an when ever i go home from hanging out i think of the perfect opportunities i had...I dream about her constantly (not perverted but just us hanging out an stuff) and when i wake up i feel so on top of the world and loved and happy and just so awesome...So some of the signs i think a kinda of flirty for having a bf is like when were watching a movie were are almost on top of each other and shes always has her legs on mine or locked with mine. She was once getting dressed an came out half naked an asked me to throw her up the banister a shirt that was on the couch in the hamper. maybe she just thinks of me as a really close friend because were always talking about personal stuff...personal stuff..not perverted but really personal stuff. I don't know what to do just about every song i hear i can relate to her or the situation im in with her an i just think of her an her beautiful smile...brown eyes....i don't think i have ever had a mad crush like this before...i know so. i really want to tell her how i feel but i don't want to make things awkward and ruin our friendship. Please give me advice an tips on what to do!!!