Just know that if you give them to someone, they will die. And really - that's not a bad thing. A quick, humane death - in my opinion - is much kinder than letting an animal drag on "until he can't go anymore". What is the the quality of life until then? For Cornish X, that can mean joint, heart, or other health-related problems.
We had Cornish x as pets when I was little, and I intend to try it again. If they free range all day and are fed in meals, they can stay slimmer. If you truly care about him you will think about what's best for the bird, and not just what makes you feel good. Sometimes, the hardest thing for us is the kindest thing for our animals. and want him to live, put him on a restricted diet, letting him eat a bit in the morning and and again in the afternoon. If he is still getting around even slowly you can get at least six more months out of him or more. Some people have ones that live to be over two years old (weighing around 20 pounds) Can you imagine how hard it must be for a 20 pound chicken to get around? Take your own weight. Quadruple it. How easy would it be for you to move? What physical limitations might you have? These birds were not designed to live that long or get that big. If he is still trying to move and is following his friends it's because he's a herd animal - they don't like being alone. he still has a desire to live and it would not be "putting him out of his misery" if you killed him. Right.You would not be "putting him out of his misery". You'd be preventing him from being miserable in the first place. He isn't keeping up with the rest of the flock because he cant. He's too heavy to get around.
OP, you are the only one who can decided what to do with your chicken. Please consider his welfare over your feelings. If you see him starting to struggle in getting around, or darkening of his comb and wattles (a sign of possible heart problems) please put him down before it gets worse. Personally, I think it's more kind to not let them get to that point in the first place, but that's my opinion. There is nothing wrong with putting a chicken down before it does develop health problems. Don't let anyone make you feel guilty about that.