Two lovers have been fighting, and the poem catches them in the worn-out aftermath. The opening line, "sore lovers play at harm," suggests that the hurt is real but also a kind of game, a pattern they slip into and know too well. The strange phrase "a horse of no stomach" is hard to pin down. Judging by the imagery, it may describe a fight that has no appetite left in it, a creature that can run but can't digest anything, which fits with the food that follows.
The second stanza turns cold and quiet. They have talked "all afternoon," and the words feel like rain: steady, gray, and chilling. By evening they sit down to "a poor thin supper," and the meal seems to mirror their relationship at that moment, meager and not very nourishing. The speaker stands back and simply observes, without taking sides. The mood is weary, tender in a bruised way, and bleak, like the flat exhaustion that follows an argument when nobody has won and nobody is quite ready to leave the table.