Although this situation is very unpleasant, and does get me down, there is one thing which always stops me sinking into depression.
My Christian faith.
And knowing that if Donald is dead, he is in heaven, made perfect in holiness, and far happier than he could ever be in this world.
I can have that confidence, because of what I know about him.
Not only that, but knowing also, that whenever my appointed time to leave this world comes (as it will surely come to us all) I will join him and many others who have gone before me over the centuries since God made this world by Jesus Christ.
Some people in this kind of situation become obsessed about finding the person, and it seems to consume their whole world, going into a state of denial. But I can say, that although I desire that Donald turn up, I can also say, that if it be God's will that he is found dead, or even never found, I can accept that, and say, Amen. Only by God's grace.
"...Faith is the substance of things hoped for, the evidence of things not seen." (Hebrews 11: 1).
"Though he slay me, yet will I trust in him." (Job 13: 15)