What to do, when you THINK you have fallen for your best guy friend?

He and I... we met freshman year of high school. He had a crush on me back then but, i turned him down kind of harshly. i regret that full-heartedly now,:/ We grew closer over the years though; hanging out, playing video games, and doing alot of fun stuff. I even got close to his mother, and i love her like a second mom:) now we are entering our senior year of high school. But during our junior year, he asked out this girl that i DO NOT like at all.... -___-" she flirted with my ex-boyfriend so, yeahh...>:/ and now she's part of our group and it irritates me SO.... like, GET AWAY from my friends!!!X( Well anyway, i'm stuck with her now and along with that, spend less time with him because he's with her the majority of the time... and lately.. it's been killing me, to see him with her. I actually started having dreams of him, of me and him, together. I also had dreams of her, one included of him dumping her. Too bad it was just a dream... But yeah, i think i may have started to realize i might have feelings for him after all. Because i was so used to him always being there, and now that she's in the picture, i'm afraid of losing him:( Just the other day, i wanted to tell him, i wanted to tell him so badly... but if i do, i'm also afraid of him rejecting me, telling me "It's too late, you had your chance, i'm sorry..."