He lets her go. He can feels she wants to go, as much as that hurts. He shouldn't make her be around him if she doesn't want to be, even if he doesn't understand what he should have done differently.

For now he'll just sit on his bed and cry for a little bit while Bud (who made a point of hiding as soon as the conflict had started) attempts to comfort him. They'll... He'll try talking to her later.