I know this isn't Oprah but...

[Beestie]

I like LJ's suggestion. But I'd buy some Haagen Daz futures and scrape together a new rent deposit just to hedge your bet.

This guy has basically put an offer on the table to you both: I'll have sex and give you a warm and fuzzy but no relationship. Since both of you accepted the deal (at different points in time), it will be hard to go back now and change the terms (e.g., drop the other girl and give me a relationship). Since your friend is still ok with the original deal, the guy has no incentive to take your deal unless he really does have feelings for you. In a way, its a good thing because the only way he will accept an "ultimatum" is if he really cares for you. Sometimes, a woman is not sure, when a guy stays with her, if its the sex or the relationship that is keeping him there. You will be spared that uncertainty (since he already has a "free sex" offer on the table) so in a way, its a very clean cut situation.

But, you must give it a try - the only thing you have to lose is not knowing. The hurt of love lost will fade. The agony of not "going for it" and wondering if it would have worked out had you gone for it will never fade.