Bonta's "Unfaithful" is a short, tightly packed poem about secret meetings and the bitterness they leave behind. The speaker and another person meet in a "cook house" again and again, "night after lying night." That phrase suggests the meetings are hidden and that lies are told to make them possible, which fits the title's hint of infidelity.
The middle lines are the hardest and the most interesting. The speaker says the meetings come "at the cost of finding hate / for what hurt." One reading is that to keep going back, the speaker has to turn against whatever caused the original pain, and that hatred is the price paid. The poem doesn't spell this out, so it's open to interpretation.
The last two lines say that "old jealousy" has been "made worse." Nothing is resolved. The mood is tense, guilty, and bleak, as if the secret nights feed the very feelings they were meant to ease. The brevity adds to this: the poem stops abruptly, leaving the sour feeling hanging.