The speaker treats wine like an old friend who always has the right answer. Whenever someone has done him wrong, or he feels wronged, he reaches for a drink and expects it to smooth things over. The title, "Mr. Fix-it," sounds cheerful, but it works as a bitter joke: the only thing he ever repairs is his own mood, and he does it with a bottle.
The last stanza shifts the tone. "Not another word / about sparing my wife" reads like a reply to someone's complaint or plea, perhaps the wife herself or the speaker's own conscience. The poem doesn't spell this out, so we have to infer it. What we can feel is defensiveness. He cuts the conversation off, and that suggests he knows the "wise answer" isn't wise at all. The mood is clipped, uneasy and quietly menacing, with the casual first lines making the ending feel colder.