Am I in Love?

So I'm 16, and there's this guy (who's also 16), and he's my best friend in the world (and has been for about 3.5 years), I can tell him anything. I've had a crush on him, and even liked him, before (when we were younger), but now I kinda feel differently about him. Whenever he's around, I just get inexplicably happy, and I wanna be near him, just because. He just left for Guatemala yesterday, and I feel this serious loneliness, like a part of me is gone. I don't know if this is just some weird thing going on with me, or if I'm actually in love with him...help, please?