In this case, absence certainly DID make the heart grow fonder. I agree that this sccene and the motel scene clinch their relationship for all time. They had just re-found one another and this time, by God, they weren't going to part and go their own way without some promises being made to hook up again. it wasn't going to be as often and thoroughly as Jack wanted, but it would have to do, and it did for twenty years, at least.
This is also my favorite scene from the whole movie because I think it is the moment when they both knew they had found something very special -- something most people never find. Whether either man wanted to put a name to it is still something I ponder, but they both knew the other one was part of them.