Dog shrink

I really need some advice on dogs who are depressed because they lost a companion.

No, I have not lost my mind - I am serious.  Our dog Roscoe has lost 12 lbs since Blue died and has regressed horribly, to the point that he has started using the inside of the house as his personal bathroom.

I think we have solved the eating issue - wet food mixed in with the dry food will do the trick.  But the rest????????  I wanna scream!

Anybody else ever had this problem before??  Who would have thought that he would miss bossy, mean, dominant Blue like this?  Unbelievable!