Discuss it with her

"Cecily" you say, still gingerly thrusting inside her, "I'm going to finish soon. Do you want it out or...in?" She seems confused. "In? That could get me pregnant, right? Is that even an option?" You shrug as best you can in this position. "Well, it's an option for you. I'll go with whatever you decide." She looks like she's thinking seriously. "I mean, if I got pregnant, that would be a disaster!" You nod. "Well, it would be hard, yeah. You could try hiding it and finding a home for it maybe; or, come up with a lie, maybe say it was a virgin conception?" She winces at the idea. You guess it would be a bit blasphemous. "I'm not trying to push you in any direction, just giving ideas." She lays quiet for a while, being rocked by your movement. "It would be bad... but it might not happen, I think. Some people try a long time for a baby. Plus, having sex without at least trying to procreate is sinful too. Either way, it's sin!" she says, tearing up. You lean in again to comfort her. "I know Cecily, but there's no point crying over spilled, uh, milk. Just make the best of your situation." She goes quiet again.

After maybe a half-minute she looks up at you, eyes-wide. "I don't know. I want you to decide for me. I trust you" she says before leaning up for a kiss. You give it to her, but now you have a big choice to make.