Should he tell her? This probably isn't the first thing one wants to hear immediately after stepping foot into another world.
Maker knows that he didn't.
"The archdemon," he says, "The only way to--to kill that thing is for one of us to die."
A beat.
"But the good news is, all I had to do was sleep with Morrigan in some sort of demonic sex ritual, and we both live!"
It's clear Alistair is Not Happy about the prospect. Especially considering his feelings on Morrigan.
"I've been here for almost a month now," he says. "And I've had a lot of time to think about things. To think about us."
There's something lodged in the back of his throat. It's stuck there, and he's not sure it'll ever become dislodged. He stands there, in discomfort, knowing exactly what he needs to say.
How is that he can kill Darkspawn, but three little words are enough to stop him right in his tracks?
"I. Like you," he says finally. "I like you a lot, actually. Not in the way other siblings like one another. Not in they way Grey Wardens, do, either. I like you. Like the way a man likes a woman."