He can ask but if he doesn’t have anything in writing he might have learned an expensive lesson about why he needs to become a judge of character...
Learning about deadbeats and how to spot them and keep them out of your life is a valuable lesson in growing up.
With limited exceptions, a contract doesn't need to be in writing to be enforceable. A contract is just written evidence of what was agreed. In the absence of that written evidence other evidence can be used. For example, if he can show they were splitting the bills before the moratorium started that is evidence of the agreement and he would likely prevail in a law suit.