How can you be sure it's just pot? Disappearing for the whole night is not typical for a pot smoker.
Whatever it is, I hope you can figure out what you want in a relationship and what your boundaries are. Don't base your future on someone elses empty promises.
Accepting someones behavior is completely different than having expectations that someones behavior is going to change based on what we want for them. There is an saying "expectations are premediated resentments." We can only set expectations for ourselves, for our reactions. Not for other people. Unless we want to be continually disappointed...
It's important to figure out what we want in a relationship and go after it, and if it's not a person who smokes pot constantly and disappears for the entire night, then the next step would be to do something about it.