Despite everything, he is utterly devoted to Walburga, supporting her through the fall out of her curse and their failed pregnancies, as well as caring for their living children.
Freeing her from the curse by disowning her was the hardest thing he ever did, but now she is free...

Arcturus discovered Finn's identity. He had Finn murdered in front of Orion.
Orion was sent to Europe, to train as a duelist and Blood Purist soldier.
When he was recalled, it was to marry. +

gained him older friends throughout Slytherin, including Abraxas Malfoy. But it was Ravenclaws Lyall and Fionnlagh Lupin he was closest too. Finn & his Rye were soon in love and inseparable. Before they could follow Wal and Mags into hiding, Arcturus using legilimency broke Orion's defences. +

In September 1941, Orion attended Hogwarts and was sorted into Slytherin House. He stuck close to his cousins, especially Alphard, but was adopted by sixth year Gryffindor, Maggie Warren as "Baby-Black". Becoming Slytherin beater in his second year, and Alphard's introductions +

Arcturus kept his children shut away from the outside world, within Grimmauld Place or the ancient hall at Blackmoor House. Their only contact with other children was their second cousins, Walburga and Alphard.

about Orion:

Orion Aquila Black was born on the winter solstice, 22nd of December 1929, the younger child of Arcturus Black, patriarch of the Noble and Most Ancient House of Black, and his wife Melania McMillan. Taking the position of Heir from his cousin, Alphard. +