Saving Orion comes with a cost. Sirius is reinstated as heir of The Noble and Most Ancient House of Black.
He agrees, with two condition, she is going to marry Remus Lupin, and the family will support them, and werewolf rights.

In exchange Orion permits Sirius and Remus use of the abandoned country Manor House (Blackmoor) during the Full Moon.
It's here Sirius discovers Orion is dying, side effect of breaking a curse to save Walburga from insanity.
Sirius now has the key to saving her father's life... +

After Regulus death in 1979, she made contact with his parents for the first time since running away from home in December of 1975.
Hearing their story, and meeting his new younger brother, Alopix, she unwillingly allows Orion & Walburga to maintain contact. +

In the winter of 1978/79, Remus moves back to London, still working for Dumbledore and the Order in the Werewolf packs, and meets Sirius again, on a miserable stake out mission. It isn't long before Sirius stumbles to Remus' flat, rekindling their hidden relationship. +

The war leave its marks on everyone, as friends die, and suspicions rise, Remus and Sirius (who never publicly dated in school, keeping their relationship secret from almost everyone) have lost contact. No longer trusting each other, fight after fight drives them apart. +

/Background:

(Canon compliant til '79)
After leaving Hogwarts, Sirius gains a licence as a freelance Curse Breaker. Working from her flat in Soho, Muggle London, he also fights against Voldermort as a member of the Order of the Phoenix... +