My best friend is an idealist and I want to convince him that a relationship between us is feasible.?

This is a tough one. I really don't advise people dating their friends. If you must broach the subject again I would probably ask him if he feels more than just a friendship there. I would caution him that the whirlwind romances don't really last (they rather burn out quickly) but that the importance of a relationship is the friendship because honestly everything else fades.