Yeah, I agree, you definately have to tell her, cos this is stronger than a simple crush, as you said it's love. But in some resepects as she's your mate she may want you to respect the fact that she's not single. Four years is a lot, to her he's not a loser- well obviously can't be, dont forget love blinds everyone and well it may have blinded her. I heard this theory about the just friends thign that girls want it for the male attention and security- in some senses it makes sense. If she's giving some signals then that could be a good thing she knows to an extent that you have feelings for her and well things havent changed that much. You think that you can hide your feelings but the fact that things havent changed maybe shows that she already knows? It could be a time bomb waiting to explode or it could do harm to your relationship. I think you should follow your heart, and then you can let her regret what it would have been like incase she says no. Good luck.