She was at fault just as much as he was. A comparison as to who ruined their relationship was meaningless because now there was no relationship left to rebuild. In all the time they were together, they had changed so much. The time they first met and the time they last met, there was a visible difference. The problem was that they both took the other as a project. His mission was to make her quit drinking. And her mission was to get him out of his shell. And whenever she drank or he became aloof, they'd be disappointed in themselves for letting the other person down. It was just a project. And this is why, when she became sober and he became an extrovert, love lost. Because the changed personalities didn't fit together. Perfection isn't real. Their originality was what drew them together but when they were changed personalities, they were not drawn to each other. Their projects were successful but they had failed because they lost each other.
She ran away from her feelings because if she decided to feel the sadness, she'd break down to never recover. He, on the other hand, embraced the sad emotions and felt the heartbreak. They were not there for each other but their successful projects helped them. She did not drink and he did not give up to resort to loneliness. Even if they had broken up, even if they would never be together, their changed personalities would always carry a part of the other with them for a lifetime. Perhaps, how they left a part of themselves in the other was the best goodbye gift they gave to each other.