In "The Knight's Tale," suffering takes multiple forms, both physical and mental. Palamon and Arcite suffer a lot from their love for Emily. Their love afflicts them like an illness, or an arrow that pierces them through the eyes and stabs its way into their hearts. (Hey, don't look at us like that. That's how the narrator describes it.) At various points, both men declare that they are suffering so much "wo" for love that they think they're going to die.
It's not just our two heroes that suffer, though. Other, lesser characters suffer too. There's the lamenting women whose husbands' bodies Creon refuses to bury, not to mention all of the people of Athens, who scratch their faces and tear out their hair when they hear of Arcite's death.
In most cases, characters in "The Knight's Tale" express their mental anguish physically, by comparing it to illness or physical wounds, or by actually wounding their bodies (the face-scratching and hair-pulling would fall into this category). In this way, "The Knight's Tale" points out that being messed up in the head or the heart can translate into actual physical pain. In the Temple of Mars, we also see how physical suffering can also be caused by war, so that love, loss, and violence become a triangle of suffering in the Tale.
"The Knight's Tale" connects love to suffering by portraying lovesickness as a bodily illness that causes physical pain.
"The Knight's Tale" connects love to suffering by showing the way in which love can cause violence.
In "The Knight's Tale," characters express their mental suffering through physical illness or injury.