He's not my type, but I think I love him

We met when we were kids, and eventually grew into best friends. I know all his secrets and he knows mine. He's the first and last person I speak to each day, and the sweetest guy I've ever met. And when I broke up with who I thought was the love of my life 6 months ago, he was my #1 supporter. But he's not my type. Don't get me wrong, he's attractive...he's just not who I saw myself with. There's definitely sexual tension between us though, and I'm wondering if he could be THE ONE. Am I crazy?