Sounds more like she needs to have someone new lined up before she's willing to give up the security of having you at home. Either that or shes trying to call your bluff on this whole open relationship thing and get you to marry her before she lets someone else knock her up.
Frankly the whole relationship sounds terribly manipulative on both sides. You both knew there was a dealbreaker between you and figured you'd just wait it out until one of you changed. Maybe she'll withhold sex, maybe you'll find some revolutionary book to teach her her beliefs have been invalid all along. Why are we sitting here trying to figure her out? If you don't believe what she tells you (whether its her being dishonest or denial or your part) what's the point? This isn't going anywhere. The sooner you move on the sooner you could find someone who actually wants to go in the same direction with you.