It felt like they'd always been together. Mudskip doesn't know what he would have done without him. Sometimes he was lazy, sure, but it was mostly a façade to cover up the fact that Mudskip was not good at being a wolf. Or at the very least, nothing he could provide was good enough. It was never the case with Marrow, however.
In the beginning it's tutoring. Marrow is strong, and even footed. He's patient. He helps Mudskip become faster, more graceful. Mudskip's mind wanders. He's his own distraction. It turns into long walks under a blanket of stars, Mudskip thanking him for all the time they're spent together, for always being by his side. Now it's something more.
It finally clicks into place when a new litter of puppies arrives too late, weaning off in the middle of winter when Mudskip isn't practicing, unfit to hunt in this weather. One of two wrong steps and suddenly he's laying by the mother's side, singing the only nursery song he knows to keep her tiny puppies calm while she regains precious strength. It turns into stories of his long walks with his precious marrow. The words fly from his lips and have the puppies hanging off every one.
When the two of them leave together, to start their own family, Mudskip knows exactly what his place in it is.