Lying in bed with a lover, the speaker makes a bleak claim: all lovers end up liars. The partner doesn't buy it. Then, in the quiet afterglow, the speaker looks into their eyes and decides the partner has a point. Not all lovers become liars, only some do. That small correction sounds like a concession, but it doesn't bring much comfort.
The real sting is in the last two lines. The speaker can't tell whether the eventual liar will be the partner or themselves. So the cynicism isn't really about other people. It's turned back on the speaker, who admits to being as capable of betrayal as anyone.
The mood is intimate but uneasy. The bluntness of "post-fuck repose" and the casual, unpolished tone make the moment feel honest and unguarded, while the doubt underneath keeps tenderness from settling into trust. The poem's short lines and scattered spacing add to that sense of something hesitant, as if the speaker is thinking aloud.