How do you know when you're in love?

I think I am in love with someone, but I'm not sure if it really is love or if I just miss him a lot. He is my friend, and he joined the army about half a year ago, and ever since he left I have missed him a lot, but also just felt different about him. Like for instance, I would love to be with him, but at the same time I just want for him to be happy, whatever that means, even if it means he is not with me. Even if it is better for him that we aren't together, I just want the best for him. I've never felt this way before about a guy, and I've always been confused about what "love" really is, I mean whether or not it is infatuation. I talk to him regularly, but I haven't seen him since before he left. Is this love or am I just infatuated/missing him lots??