Ink
You saved him from the cold and damp place you had found him in. He already trusted you. You also let him paint with your art supplies. You also fed,bathed and kept a roof over his head. He was happy enough.
Fresh
It took a while. But he finally stopped trying to kiss you for a weird reason. So more like he had earned your trust.
G sans
You basically spoiled him. That was enough for him to actually trust you.
Storyshift Sans
You saved him from a garden snake.