"Your wife needs more love."
Translation:Twoja żona potrzebuje więcej miłości.
In Nominative and Accusative.
Nominative: Ja wiem, że to jest miłość (I know that this is love)
Accusative: Wczoraj spotkałem miłość swojego życia (Yesterday I met the love of my life)
Miłości is the genitive, and follows quantifiers, such as więcej, mniej, dużo, mało.
"wasz" is the wrong form, as it's masculine. Grammatically it should be "wasza", to match the feminine noun "żona".
This is one of the the rare examples when we don't accept both the singular and plural version. "Wasza żona" means that she's a wife of at least two people, so that's polygamy. Even if it's possible in some cultures (not in Poland definitely), rejecting it may help some people remember that "twoja" and "wasza" don't mean the same thing. Also unlike Russian, French or Ukrainian, "wasza" is not a formal way of speaking to one person.