He came from a far away pack, his memories are lost to him. All he can remember is waking up, looking different, and finding himself in the woods. He was discovered by a few hunting wolves, and brought back to the pack by them, with concerns for his injuries, which he didnt even know he had...
He eventually fell for the pack leader, promising to offer his eternal love to her,
but only with the condition that he be allowed to continue his own bloodline when she is unable to. It was a personal decision, and one that worked perfectly for them both.
It may say they are not a pair bond, but those are only the customs for organization... To show their eternal connection, they would wear permanent, matching garments.