The Marriage Ambush

Seb is partially disabled, gay, and resisting moving in with his largely-heterosexual new love Lars. Lars has an ex-girlfriend, a traitorous ally in the shape of Seb's best buddy Leah, and two kids who are willing to go to any lengths to acquire an indulgent and gullible second daddy. And one of them is gender-dysphoric. Seb's counting on getting out of this without parental responsibilities and a ring on his finger.
But what are his chances, really? Short, approximately 10500 words.