As much as i hate quoting myself:
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Iron Rule of Tomassi #3:
Any woman who overtly makes you wait for sex, or implies by her actions that she is making you wait for sex; the sex is never worth the wait.
You are not her highest priority; there are other considerations she is observing in light of her changing one of her rules. Regadless of whether or not this change was prompted by a pregnancy scare or some other reasoning, the rule has changed. Her desire to be intimate with you has been superceded by some higher priority.
Play this out to it's logical conclusion; for sake of argument lets say you did convince her to have sex with you after implicitly telling you she was now 'saving' herself for marriage. It's you that will now be the villain for 'tempting' and 'coercing' her into having sex with you after her virtuous protesting. Do you really want to be with a girl who's impulse is to resist you rather than desire you?
Or play this scenario out; You decide to obey 'her rules' and maintain the relationship in as sterile a form as you can, by repressing your sexual impulse for as long as it takes for her to 'come around'. How long do you think you could hold out? Because essentially you are making a bet with her that you can remain celibate and faithful for as long as she deems necessary for her to marry you. How long would you forego your sexuality to prove worth to this woman?
And the last possibility is that you will indeed marry this girl and have 'legitimate' sex with her in the future. Can you honestly say that this woman is worth the sacrifice in light of the fact that her impulse is to resist rather than desire you?
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Assume for a moment you felt the altruistic conviction to join the peace corp and had to be apart from her for 2.5 to 3 years doing aid work in Africa. How do you think her attitude toward you would change in that time? This girl wants the security of having you around as a surrogate boyfriend without the necessity of having to reciprocate any intimacy. Again, follow this to it's logical end, will you think it was time well invested in remaining celibate for up to 3 years if she does in fact develop feelings for someone else and breaks it off in that period? How will you feel about foresaking other opportunities with other sexually available women in that time? Do you realistically think that the quality and frequency of the sex you do have after up to 3 years and marriage will justify abstaining? As a married man I can tell you that even under the best of circumstances, frequency and passion decline in marriage for women. I've yet to meet the married guy to tell me how much better and how much more sex he was having with his wife now. And yes, even the religious ones - it just takes a year or so of marriage. You've experienced this yourself.
These are pragmatic decisions you need to consider. Turn off your emotionalism for an hour and really follow thins out long term. You know yourself far better than you think you do. I knew from day one that if I were to get married it was going to have to be with a woman who would stay fit and sexy well into the rest of her life. That might sound 'shallow', but I know myself well enough to understand that if I was going to stay faithful to any woman she'd have to be exceptional. Stop and think about what you need long term. I would guess that wouldn't include women who say one thing and behave in another way.
The problem you're encountering now is a Catch 22. If you stick it out with her you're a fool, especially if you waste a year and a half to 2 years of time and effort only to have her feelings change - yet if you remove yourself (as I think you ought to) then you are a 'shallow' jerk who was only into her for her vagina and sex was your highest priority (which, in actuality, it always is). Do you really think a woman willing to put you into this dillema, especially after fvcking you prior to it, would make a good wife? If she's comfortable in playing a shell game with her sexuality, what makes you think she wouldn't do so in other aspects of your life until, and after, marriage?
Look, I understand religious convictions, I'm a Christ-follower myself, but we're all sinners in one regard or another and we're all hypocrites in some way. This isn't about that, it's about being forced into a position where you need to think long term and from what you've described this girl doesn't meet with any acceptability.