My Bestfriend is in love with me

I need advice. I'm 22 and I've had not so great relationships. I have a best friend and we met back in high school. He took me to our senior prom and we went as friends. We've never been anything more. He would distance himself when I got into my relationships, but through it all... he's been my rock for about 6 years. We'd always somehow find our way back to each other. He's seen me at my worst and somehow still thinks the world of me. A few months ago, he admitted to falling in love with me throughout our journey as friends. He also told me, that if it were up to him, we would be married within a couple years and starting our lives together. I can't say I was surprised, but when he asked how I felt... I didn't know how to respond. I'm not attracted to him, physically. Emotionally and mentally he's everything I would dream of. I hate to sound shallow... It's not just about looks. But I feel like I've never been sexually or physically attracted to him. Has anyone been in the same situation? Thanks xx