Because it was awkward to be at a wedding as a couple and know that the probability of you ever being married was far too low, even though you both wanted that, one day, in the future. She had seen the guilt in Draco all morning; evident in the way he'd been so quiet but so unexpectedly attentive, the way that – once he'd given in to the idea of attending the wedding – he'd been so biddable, not arguing with her or even snarking at all. He felt guilty, she could tell, and although a part of her thought a fierce good and hoped the guilt would make him change his silly, stubborn mind, most of her just didn't want him to feel awful.