How is "The Forsaken Merman" suitable as a title?

"The Forsaken Merman" by Mathew Arnold tells the story of a male mermaid, a merman, whose wife abandons him and their children. At the beginning of the poem, he asks their children to call her back, but she is too focused on reciting the Bible in the church to hear them. The merman takes their children closer to the church, to the graveyard, but the priest closes the church door.
It seems that his wife has chosen God and life on the land over her family and life in the sea. However, her choice does not seem to have been a simple one. There is a suggestion she is at least part human. As the narrator states, she tells him,

I must go, to my kinsfolk pray
In the little grey church on the shore to-day.

She goes for the day and never comes back. When they see her in the church, the narrator comments on how she has a "sorrow-clouded eye."

The poem ends with the narrator saying,


She left lonely for ever
The kings of the sea.