Guinea Pig Decision Help?

So, i've had my male guinea pig Spud for about 2-3 years. Ever since we adopted him at 3 months old, my other guinea pig Demetri never seemed to like him. We have kept them in different cages their entire lives. Demetri seems fine with it but i've started to notice Spud has been lonely. He's very well tempered and the sweetest thing. I know guinea pigs are herd animals and they should be together but these two can't seem to get along. I've started considering that I should return Spud to the adoption agency we got him from so he could have a another chance to a happier life. We treat him like royalty here but I can't stand the fact that he's still not deserving the life he should be having. The only thing i'm worried about is the way they'll treat him in a new home if he even gets re-adopted. He's pretty old and adopters look for young guinea pigs most of the time. Also, it's breaking my heart to think that he may be abused or unhappy in his new home. Please help, opinions or ideas would be great! Thanks.