Sirius Orion Black III
He wanted to save his brother.
He wanted to leave and take Reg with him and never look back.
Andy had saved him from being tainted and he wanted to do the same for his brother.
By the time he got the chance, it was too late.
(It was wrong, he knew, and he did love her, he really did, but sometimes, occasionally, when he was sitting in Grimmauld place...
Sometimes Sirius wished his baby cousin was really his baby brother)