He looked at the bottle of pills on the passenger seat. For a moment, he thought about the bridge, or the bottom of his pool, or just driving until the road ran out. He had spent his whole life trying to be "good," or at least trying to be seen as good, and every time he reached for it, he ended up hurting the people who actually cared. He had called Diane, but the conversation had left him feeling more hollow than before. She was moving on, finding a version of happiness that didn't include his chaos, and he couldn't blame her.
If you'd like to explore different aspects of this finale, we could look into: during her final phone call with BoJack [S3E12] That Went Well
about his own identity and his future with Emily He looked at the bottle of pills on the passenger seat