Graves is an omega but keepts it a secret through suppressants and faking his scent, masquerading as an alpha because he wants to have a career. He met Theseus during the war and they became bff, with Theseus eventually finding out his secret and their relationship progressed to becoming bondmates in the midst of the war. But even bonded to Theseus Graves doesn't want to abandon his dreams for a career, so he leaves him and goes back to the States.
Fast-forward - Graves is discovered in Grindelwald's dungeon, pregnant with his child, because his suppressants ran out during his captivity and Grindelwald took advantage of his heat. The revelation that Graves is an omega masquerading as an alpha in order to attain such a high post in the government causes a huge scandal. Graves is fired, all his possessions are appropriated by the government. In order to save face Graves' family publically disowns him. Graves ends up lost, completely alone, disgraced and pregnant with a dark wizard’s child while bonded to another man.
This is the actual prompt (but you can write the backstory if you’d like, I’m more than up for it):
Newt, who knows that Graves’ is Theseus’ bondmate, finds him and offers to take him back to his brother. How will Theseus take this arrival? Will he accept him or reject him? Graves, broken by scandal and captivity, is completely submissive and contrite when he arrives, waiting his bondmate’s judgement.