In this game, Gray has more likes.. and dislikes. He seems to like a lot of things. So give him eggs and stuff. He also seems like to like fried rice. But he hates onions. I still have to do some testing and find out some more stuff he likes, so stay tuned.
His birthday is Winter 6th, so be sure to give him a gift!
Also there is a special cutscene involving him, you.. and Mary, sort of. In Fall of year 1 or 2, on almost any day up to the 27th, he'll ask you to use your mill so he can make a hammer. After a couple days, he'll ask you to use the hammer, and it'll break. Mary sees and they get into a fight. Gray will later thank you and your friendship with him will go up.