Even though all these characters talk big most of them stand alone / are lonely at heart. For instance, George is one of them as he uses Lennie as his company and that's his drive through this journey; keeping out of trouble represents his care for him and their undeniable good friendship. No matter how many times he says how good it would be alone he'd truly rather have Lennie by his side as in why he keeps Lennie with him through everything he put him through. As the other character Candy, in this case doesn't want to put his dog down because he's already feel alone and will feel more lonely as the dog is the only family Candy really has anymore and putting that dog down even with the offer of new ones it wouldn't feel the same. All George has to do is keep Lennie around and better the friendship. They have then he won't feel lonely and Candy needs to get a new friend to get close with so the pain can at least semi go away.