Best friend since 7th grade, and now I'm experiencing feelings for him...?

That's cute. I think it's normal to fall for someone after living with them for some time. You get to know them in and out. You're like a married couple without the actually intimacy and all the other things the come with marriage. If you like him and he likes you (which it seems he does) go for it! You already know him well enough, so not much will shock you. Good luck.