He was no stranger to the concept of spilling one's private thoughts to near strangers in emotionally stressing situations. Merlin knew he'd spilled parts of his own story out in a random pub encounter shortly after leaving the ship he'd worked on to try and settle outside Lisbon. As he'd learned then, sometimes the less one said, the easier it was for someone else to deal with their own emotional fallout.
So, he sat quietly and just let the other man speak for a moment.
"Sometimes strong enough emotion doesn't really care whether other people are around or not," he said gently. He wasn't sure what Vaisey meant about not being much of a father, although he remembered what the auror had said about understanding Remus' position the night he'd come back and learned about Ted's existence. "I don't know about your past, but I'd say you're doing well enough at fatherhood now. You're here."