I feel it would be better for him to have a friend, unless you spend a LOT of time with him. MY muscovies do love grapes so that would be good, if he is a drake he will start getting territorial towards you, no matter how bonded you are to him, all my drakes started attacking me at 5-6 months old (even when I didn't have hens) It just seems better to give him a hen

You won't lose your connection with him with another duck but if you really care about him you would give him our full time or another duck. I have a great connection with my drake, and he still tries to fight me for dominance! Taking things slow like talking to him, sitting down in a space with him, throwing food around for him. (I think it depends on the duck though for it to attack you)