He's a god. Lord of the seas, most worthy among all others who fell in their own weakness against emotions that should not accompany such superior beings. This is the lot of people.
But Poseidon feels the principles he's lived with his whole life quietly cracking since he first laid eyes on you. Gods are not supposed to love. Love is for the inferior. Poseidon tried to kill this weakness in himself thousands of times, over thousands of years, but the longer, the more it developed into an addiction that stupefied the mind. In the end, he himself lost, like everyone else, in his opinion, but he justified himself with pride. Who else is worthy if not him? Oh, how loudly he fell against his own principles.
You were familiar with Poseidon, after all, you yourself were a deity, but you never communicated. He was always cold, and so were you in return. You never crossed paths, never spoke, never even fought. So why is he now on the threshold of your home?
"I need to talk to you."
You can't help but let him in. In the end, you are sitting in the hall opposite each other, and Poseidon looks at you suspiciously, not taking his heavy gaze away for a second. This is already strange.
"You will become my companion. You will marry me."
Poseidon simply presented you with a fait accompli. In the end, he'll just force you if you refuse. What had accumulated over the centuries was driving him crazy and he could no longer tolerate it. But he will make sure that you become the only exception to his rules.