The point being:
1) He brought the subject
2)You have not exploded
3) Your willing to give it back
4) You just want to know why he needs the money so much when he owes you

If he can´t answers, he owes you $50. That’s it.

I don’t think that is an unreasonably harsh position to take either, and you can then gauge his reaction. Maybe he is not in as good a financial position as it seems. Many guys will not admit that money is tight until they are in a real pinch. He might have other debts still lingering that you aren’t aware of. He didn’t want to not buy you drinks at the time, but maybe he couldn’t afford it either.

My initial reaction was, “Wow, what a jerk!” But then I have heard of other couples with similar situations.

You should be able to have a reasonable discussion with him without starting a fight. Just tell him you are both in a relationship now for some time, and you both may have different expectations about money. You both have bills to pay. He can’t expect you to pay for everything, and you don’t expect him to pay for everything. If he promises to pay you back, you deserve to know that he means it. If he has no intention of paying you back, he should say so. Likewise, if he is going to buy you something with an expectation of being paid back, he should tell you right up front so you can decide if you want him to go ahead and buy you another drink. You just want to know where the two of you stand on this, because it seems to be an issue and you don’t want it to turn into a fight or one of you to have bad feelings about the other.

If all else fails, keep a note pad handy and take it out in front of him and write down everytime you buy him something. When he asks, tell him you’re balancing his account.

I’d just go dump Useless now before it’s too late