1/2

Not sure how much choice women in Ishgard have regarding birth control, but I can't imagine they'd plan having a child with a man they can't marry because of his position. The NPC women in Ishgard give us a very medieval image of marriage, so having a child out of wedlock is probably a terrible sin.

Likely motives for a woman to bed Thordan could be a misplaced hunger for power, or being attracted by power, if he already was Archbishop or close to becoming it around the time. On the other hand, Thordan doesn't strike me as the kind of guy who'd be above rape or whoring and the lack of affection for his son gives us an indication that he wasn't in love with Aymeric's mother.