False hope will only do harm. If his plans for this particular girl have no future, encourage him to look for someone else and to seize the day with them. Plenty of other fish in the sea, and stuff. And even for the most awesome guy in the world, some women just won’t suit him. That’s nobody’s fault. Just try someone else, there’s bound to be someone you could make happy. It will be more difficult than either encouraging him to be brave and try his luck with this girl or allowing him to give up altogether, but it would be the only right thing to do, I think.