Keeper Marethari had been married, once -- when she was the First, she was married to her Keeper's Second. The Keeper and his Second were killed when my clan was in the Frostbacks, and Marethari brought the clan to the lowlands and became the Keeper herself.

[ It still hurts to talk about Marethari, her clan, but this is more of a soft sting. This was history even when her clan was alive. ]

The Dalish want mages, and since the Keeper is always a mage, it makes sense for them to marry -- or to have children, at any rate.