Should you tell someone you love them?

Should you tell someone how you feel regardless out the outcome, even if you know they will just reject you?? I am absolutely besotted with this girl, I have known her for about 3 years and we have been really really close friends. The big problem is that she has also had a boyfriend for the last 3 years. I have never met her boyfriend but I see that they absolutely love eachover. So even though me and her are very very close friends I would never compare.So I have allways kept my feelings quiet because her happiness is more important than mine. But things have become so awkward for me in the respect that I dont know if shes leading me on or not,I know sometimes girls give off the appearance of attraction when really they are just being friendly. I mean she will happily cuddle up with me or hold my hand or touch me plus when we talk for me it just seems so right and easy. At times shes said suggestive things to me in the past about love and shes also said that she thinks I am attractive and stuff. I have no idea if shes just being friendly,teasing me or she genuinely likes me back. Its horrible because I dont fall people easily and I cant think about anyone else we have so much in common. I feel its so unfair how someone I feel so much for feels for someone else not me.Idealy I would love to be with her but I respect the fact she loves him not me, but I have never told anyone how I have felt about them and I am 24 and I need to do it so my head wont be so messed up. All I want to say is "I know you have a boyfriend but for now just let me say your perfect to me and my wasted heart will love you" is there anything wrong with that?? I mean at least I can then I can phase her out right???