What is he doing?

After saving you from drowning, he should've let you go. But when he sees you with no memories of your past or who you were, so dependant on him as he whisks you around in his watery domain, powerless to stop his whims, just gives him a high he can't quite let go off. He wants, no, needs, you to stay dependant on him.

"Don't worry about your past," he murmurs, keeping you hidden deep in an underwater cave. "I'll take care of you, so just stay with me."

A demand.