Lots of great advice given so far. Just want to add another voice to the chorus that's telling you to be up front and explain everything. It's fine not to want to have sex, as long as you're up front about it. I was married to a woman who wouldnt have sex for years at a time. Without going into all the issues involved, if my expectations had been set correctly...perhaps we could have worked through it. A lot of times people think they're being polite by not expressing themselves, when they're actually doing more harm this way.
You and your pregnancy definitely deserve to be taken care of by all involved. I'm sure that she'll be just as happy and comforting to you as you have been to her.
Me - male, 42, poly, straight, in a serious relationship with Audrey, also casually dating.
Audrey - female, 20, poly, pansexual, also casually dating.