Yes, it would be best if you could find a way to keep him. It's hard to find a home to take an 8 eight year old dog unless you had someone in mind. If he is depressed now, how do you think he will feel being taken from his home. Does he live in the house or outside? If he is an outside dog I can understand why you would think he would get lonely, but if he is in the house and part of the family then he should still have enough socialization to be okay. However, if you can provide him any attention look for someone that would be ready to take on an older dog or take him to a no kill shelter where he is more likely to be adopted. I know it is a hard decision. Best wishes.