My best friend thinks I'm in love with her, how on earth do you react to that?

She and I (female, btw) have known each other for a good five years. We did all that friend stuff- going to dances, sleep overs, the works, but there has always been an inequality. I'm the accommodating type- I was painfully shy when we met, and have always been genuine and open with J. I am bisexual- I have made no efforts to hide that, but it has never had much of an effect on our friendship. Let's say there's a movie coming out that we both really want to see- I'd be the type to call and say I bought our tickets to the midnight showing, and that she can pay me back next time i see her. J would be the type to buy the ticket, tell me she's going- and if it's already sold out- too bad for me. I've put up with that kind of BS for years because "that's just the way J is" Recently, I've realized how unhealthy it is and distanced myself from her, but it didn't quite work out(yet). I should mention that we have kissed before- but that's as far as she was willing to take it. I agonize over why I could possibly let myself be treated so selfishly for so long- had I enabled her? Probably. Felt like I deserved it? In a sick sense- yeah. But today she dropped the bomb. J asked if I was in love with her. In love? I mean, we say "ily!" in texts, hug, etc., but in love? Could that really be the reason I up up with her shit for so long? I guess I don't really know what I'm asking you guys, I'm just terribly confused and conflicted- I would appreciate any advise or related stories you feel inclined to share- thanks.