Just go out like you always would under the guise of friendship and instead of this ultimatum you are basically setting up try to get into his life more... on a personal level...

see his reaction when you "act" more like a GF and you will know if this is the right path for you both.

If he is shy and has money, he may be into prostitutes. Just saying.

If your there enough, around him more, as a guy, drugs or alcohol or whatever... he will slip up and do you eventually. Then you got him girl!