"is it normal that i am in love with my best friend?"

For the past 4 years I have been in love with my best friend. I have tried to shake it off and not think about it, but I can't! Everytime I talk to a new girl or go on a date all I do is think about my best friend. I compare every girl to her, and no other girl is near as amazing as she is. Unfortunately my best friend has a boyfriend.
My best friend Alex(shes a girl) we met freshman year, and i thought she was absolutely amazing looking. So I told one of my friends on the football team about her. He was like, "Yeah dude I'll hook you two up." Than he goes behind my back and dates her, and they have been for the past 4 years.
Alex and I talk all the time, we are SO close. Her family loves me, she loves me. Her cousin lives in Georgia and every now and then she will come down. Well Alex's family and I have this on going joke that I will marry Alex's cousin. So you know I do alot of really sweet stuff for Alex's cousin, I am so romantic and sweet and good too her. But the message I'm trying to rely across is, "Alex this is what Id for you, not your cousin". Its confusing.
I am so sweet and romantic to Alex, like she tells me all the time.."Adam you are so good too me, to bad my boyfriend can't act more like you". We talk alot and sometimes when we talk Alex will be like, "I can't live one second without having you in my life". I took her skating the other night and when we got back it was late and she was like,"Adam don't leave, I want you to stay, I want to be with you and see you"..Alex also says stuff too me like, "Alex, I need you!, you are the most amazing guy inmy life."
Her family tells me secretly that they think her and I would make the best couple. Its really upsetting because I'm leaving for college to a different state, and she is going off to college with her bf. We're both leaving within the next 4 months. She is really upset about it and so am I. But than again maybe its a good thing, I'll take all the pain if thats what it takes to keep her happy.
If you're interested, there is sooo much more to this than what I typed. Just leave me a message in a comment and I'll give you my email so we can talk more about it. Any advice would be more than appreciated. Thank You!