@Tamerlane
He finally knows he let us down, that he has been a fool to himself and that he thought he could live for no one else (but himself). Now, through all the hurt and pain, he's come to respect that the ones you love mean more than anything, so, with sadness in his heart he feels that the best thing he could do is end it all and leave forever. What he has done is done, it feels so bad. The happiness that existed now is sadness, he would never love again and his world is ending.
He wished he could turn back time (through world B), because all the guilt is his (World A's demise), he couldn't live without the trust from those he loved. Despite knowing he can't forget the past, or love, or pride. In the end, it's killing him inside.
Something something, tumbling down...