Hi Osier,
The truth is painful, but much less painful than waiting with hope. He will find out the truth sooner or later. The longer you wait the worse it will be for him. Each day that he goes on with hope is a day that he gives a little more of his power away.
It's like putting your money into a slot machine hoping for the payoff. When you realize there will be no payoff it is too late becasue you are left with nothing.
If your serious and sure that this relationship is over then the kind thing to do would be to cut all contact.
Maybe after a few years you can be friends again. I have a good friendship with an ex-boyfriend after cutting it off for 5 years.
It just might make things easier on you too. This must be sucking the life out of you.
Hugs and thanks for your support,
MG