I wouldn't question him about whether he can make this 4-year commitment, or pin him down on the R. I'd point out that this will be cost for the next four years plain and simiple and let him figure out the rest.

If he's worried about it let him bring it up. I think it's better at this point to live your life like he'll still be there... and if he leaves he'll just have less money for dates. No fancy dinners!!! It will be boxed macaroni and cheese or Mc Donald's!

There is no arriving, ever. It is all a continual becoming.