He is the villain. He's not pure evil, he's just a bit of a loser and lacks self confidence, but many times he is given a choice to do the right thing or the thing that benefits his own wants, he makes the selfish choice.

That's why he's the villain. Little by little he knows things are going wrong, but he's a "nice guy" and surely he deserves something he wants because he's "nice."

The movie is a fantastic depiction of what is wrong with NiceGuys™ and that they actually don't care nearly as much about the other person as they think they do.

The director himself said it best, "The One Wish Willow isn't cursed, the shop owner is meant to demonstrate that you can make your wish and live a fine life after. Bear is cursed because the wish he makes is cursed."