My input is that he should not have proposed if he wasn't 100% sure he wanted to get married.
If it were me, I would hand back the ring and ask him to ask you again when he is sure.
I definitely would postpone the wedding, either way. You don't want to make him feel "forced" into marriage or like he's making a mistake.
I am not a fan of that kind of immature behaviour. Sounds like somebody needs a few years to grow up.