I think i'm in love with my best friend.

Don't be blind. If you denied him 1 year ago for "your friendship" which would be a normal answer from a girl in your position, can you truly expect that your feelings are real?
He has a girlfriend now. Don't you think that jealousy is indeed a crafty tool?
I'm not denying that you might love him, but he has a girlfriend and it is therefor cloudy. Even from sheer respect to others you should wait. No one waits too long for love. Matter of fact, those who wait for love, experience it's true form.
I also had a "lady-best-friend" and we were close and we might even be more then friends in how we acted. We were always touching and kissing at parties but we never did anything.
What I knew was that if I had gotten a girlfriend, she would make a move, so I kept such things secret. I loved our half platonic relationship and what I want to tell you is that I still do love her. If there comes any time in my life where are paths cross, I will not hesitate to create a new bond for a real relationship.
History is strong my friend, let the chapter pass so that a new can unfold. You never know were it might take you.

And yes, it is normal.

I agree with mtnw. I think u should find out first
how serious he is. I think if he's been going out with that girl for two months is serious so yo should try to forget him and meet other guys, there are a lot who might want to go out with you..

timing is everything, isn't it.

you know, falling in love with a friend always ruins the friendship.

i suppose, being such good friends, you can ask him how serious he is about his current girl. depending on his answer, you will know what to do next.

at this rate i think u will might lose him...or he just going out with her to make u jelous

I think we're meant to fall in love with our best friend of the opposite gender. Your soul mate should also be your best friend, not some person you asked on a date because they looked good