Spoilers For Season 6 Part 1 Of BoJack Horseman. Throughout BoJack Horeseman, Diane often found herself being asked to take care of others before taking care of herself. But in Part 1 of Season 6, that all when changes when she meets a buffalo named Guy, a cameraman on her show for Girl Croosh. Lakeith Stanfield (Atlanta, Sorry to Bother You) voices Guy in BoJack Horseman and he delivers a calm, occasionally soothing vocal performance that makes it easy to see why Diane is so attracted to him. After years spent trying to manage the emotional ranges of people like BoJack Horseman and Mr. Peanutbutter, someone with a relaxed and confident demeanor like Guy is a welcome change of pace for Diane.
However, falling for someone who seems to have his life together — as much as any buffalo can, anyways — forces Diane to recognize that she needs to start working on her own mental health if she wants to build a healthy relationship with a buffalo like Guy, or anyone else in her life.
When Guy is introduced in Episode 3 of the show's final season, "Feel-Good Story," he and Diane have been hooking up while driving cross-country [to] film videos for Girl Croosh. After the two get serious and start talking about the possibility of Diane moving to Chicago with Guy, she makes the brave choice to stay out of a relationship for both of their sakes.
"I feel like the whole world is pushing in on me, except for when I'm with you. You have been such a good thing for me," she tells him, before dropping that she can't be with him if he's "the only good thing in my life."
However, Diane doesn't stick to that decision for long, calling Guy to let him know that she's willing to give the relationship a try. She moves into his Chicago apartment after Girl Croosh is bought out by a conglomerate, and her unmedicated depression starts to affect her and her relationship with Guy. She stops taking care of herself whenever he's not around, and contemplates breaking up with him before he gets a chance to see the "real" Diane — which in her mind, is the Diane that can't stop leaving pizza boxes everywhere and doesn't feel she deserves someone like Guy in her life.
After an emotional conversation with BoJack when he comes to visit in Episode 7 , she finds the hope to turn over a new leaf. She takes action to show Guy that she cares about him and is willing to listen to his advice and start get on anti-depressants in the name of self-care. It's a happy ending to the half-season, but it's not an ending to her story. Progress isn't something that happens with one gesture, no matter how kind that gesture is. In the second half of the season, she may learn the hard way that improving herself better for someone else's benefit, especially when that someone else is "the only good thing" in her life, is much more difficult than showing up at the airport to pick up Guy one time. As a wise monkey once told BoJack, "you have to do it every day. That’s the hard part."