Why is my neighbor's wife here, even though I have a wife? (JUR-268) A well-meaning mother friend proposed a 3P to "fill the void in my sex life."

I've been married to Kanna for many years, but lately we seem to have drifted apart, and our sex life is nonexistent. Our only solace is the Satsuki family next door; as a senior to us, they always help take care of us. One day, when my wife and I were arguing, Ms. Satsuki Fumino intervened to mediate. Kanna seems to consult her at night, and I feel responsible. I felt embarrassed by her gentleness. I stood there, shrugging, when suddenly Ms. Satsuki Fumino said, "How about this! I'll help with the sex!"