He sees all that he Didn't do in the relationship to meet her needs now that it is almost over and he feels that it's too late. It scares him that he won't find this love again. He's beating himself up because he knows he didn't tell her how he felt & didn't give her what she needed from him. He's scared that he made the wrong choice not telling her, he's trying to move on but he can't because he's second-guessing the loss of the relationship because he still loves her & he's hurting, wondering what could have been if only he hadn't been so stubborn and selfish and more open with his feelings. He can't move on because he keeps thinking he could have, should have done to showed her more love and wondering why he didn't do it because he really loves her. He's so sad because he can't figure out why he didn't know all of this before it was too late.