Flint was meant to be nothing more than a mask, a facade to be worn and cast aside when the time came. Except he wasn't. It had been James McGraw that was thrown into the sea without a second look. There was no one to mourn that man, no one but that shadow of him that lingered within Flint.
Thomas was a stranger, for all the power he'd once held over James McGraw—and the thousands more that cowered below Flint's wrath when he murdered in Thomas' name—he couldn't name Flint for what he was. To Thomas, he was James, McGraw more so than Flint.
There was no peace among these landbound men, possibly a shallow happiness by an old lover's side. He should have been pleased, maybe even joyous if he were a man inclined to feel such a thing, but he isn't. That scrap of McGraw hates him for it.
He longs to return to the sea. Flint doesn't want to die here, beside a man he can no longer love as he should. He stays with Thomas anyways.