Most Helpful Guy
Whenever you take on the role of "running" things, you end up with the responsibility for things being run. He's dragging it because you're nagging. You're nagging because he's dragging.
Stop trying to run him. There may or may not be a future for you, but you got to stop running him, managing him. Stop being responsible for him. Let him be responsible for himself. Let him be late, wrong, bad, whatever all by himself. Concentrate on the stuff that you do yourself. That will either make him shape up, or drop out. Either way is preferable to what you've got going now.
And remember, just because you decided something, didn't mean that you actually AGREED on anything. Just because you put up an ultimatum doesn't mean that he has any stake in the decisioin. One cardinal female error that is repeated over and over again is that you believe that something is agreed on when it is simply you who have expressed a wish, and assumed compliance.
If you decide something, assume that he's into it. If he is not coming, not doing his part, go on without him, AND WITHOUT THE STUFF HE WAS SUPPOSED TO DO. Leave him behind. Leave his behind. Do stuff on your own.
BUT NEVER EVER do it out of spite. Or to punish. Just do it when the situation requires. If you start "punishing" him, you just leave him right now. That is just evil.1