Lord Vishnu is married to Lakhsmiji . After marriage he preferred to stay with goddess Lakshmiji in the Sea . The Sea is considered as Father of Lakshmiji.
So what made lord Vishnu stay in the sea?
May be your are referring to Lord Vishnu's leela about the Nachiyar Koil . You can read more about the temple and the preciding deities. It is said that the Lord appeared in Venkateshwara form to marry Lakhsmi, but as demanded by Lakshmi the Lord should stay with Her and not the opposite where the bride goes to the husband's house. Probably this question will further answer your doubt.
Vishnu stays his in his place Vaikunthaloka, just as our bhuloka has oceans Vishnuloka has Ksheerasagara. He stays there according to Puranaprakriya. The ocean where Lakshmi was born is situated in earth. This ocean is in Vaikuntha. The question itself is not right.