During Graves's captivity, he began a sexual relationship with Grindelwald. It could be because of Stockholm syndrome, Grindelwald forcing or coercing him, a soulmate bond, or whatever the potential filler wants. However, post film, Graves realizes how fucked-up their relationship is/was, and chooses not to have any contact with Grindelwald, not visiting him in prison, not being present at the trial, etc.
When Grindelwald escapes, Graves is worried, but decides to keep trying to move on. Eventually, he decides to try dating again. He gets set up with a man or woman and they're on a date, when the restaurant they're at is attacked by Grindelwald and Grindelwald kills Graves's date, then takes Graves back to his apartment for a talk about how Graves isn't allowed to 'break up' with Grindelwald unless Grindelwald says so.