Why does Wyn return to Montana in the novel, Happy Place?

After Wyn's father suddenly passes away, he moves back to Montana to be with his sick mother and his sisters. He misses Harriet, but he hopes that breaking up with her will give her the opportunity to be happy. He takes the time alone in Montana to work on himself. He starts taking medication for depression and even begins a furniture company that starts making him a large amount of money.