my friend accidentally fell in love at me

I've been in your girl bestfriend's situation before. I accidentaly fell in love with my bestfriend. But it's been almost 10 years now since I told him about my feelings and guess what? We're still friends. It's not impossible to happen with you too. You can still remain as friends if you both don't give up your friendship. We had so many troubles that we encounter before but we didn't give up. He let me understand that we're not meant to be lovers but as friends. Though he didn't accept me as his lover still he shows how much he value me as his friend. So it's just simple as let her feel how much she mean to you as your bestfriend. It may not be a love as a lover but a true friend. If she truly understand then she's really your bestfriend.

A very tricky situvation. but be frank & tell her your intentions.afterall she is your best friend.i dont think you would hurt her.

Well, that's a hard situation. If I'm in the place of your bestfriend I'd rather hide what I feel so that you will not be confused....I think your bestfriend doesn't want to pretend anymore...maybe she is already tired having a friendship full of pretensions...and maybe she is also tired of seeing you together with the other girl...but you should tell her what you really feel for her...tell her that she is a best friend for you...yes, of course it is painful but at least you told her the truth ...and never cheated her...for me I'd rather be neglected than to be cheated by my best friend...