I'm not sure I'm entirely following this, but the answer to the above question is that, if no laws exist with respect to a particular situation, it's because the legislature hasn't enacted a law, and that's because either the legislature never considered it or did consider it and decided not to enact such a law.
I don't know if a law exists or not. That is what I'm trying to inquire here. I doubt there is an explicit law regarding this exact scenario but trying to see if it falls under an existing area of sexual assault.
Again, using possibly the most extreme example I can think of (poking holes in condoms or swapping out someone's BC pills with fakes), then trying to work down from there.
In other words, IF swapping out someone's BC pills with fakes is illegal, covered by some degree of rape or sexual assault, then that's something I can look into and see if it fits my scenario.
Given some of the crazy arguments that have gained traction in this area, it wouldn't surprise me at all if someone claimed rape because the consent was based on the use of birth control, and lying about the birth control negated the consent.
What were the terms of the agreement?
She would consult an OB/GYN to begin a medicinal birth control regimen. We would share the costs. We would discuss if anything changed.
Similar to a typical, pretty much implied, agreement with condoms: "I'm gonna use this condom. If it breaks or if I suspect it fails, I will let you know so we/you can act accordingly (morning after pill, Plan B, paying especially close attention to missed period, etc)"
What were those actions?
Not using other forms of birth control.
Not paying special attention to her menstruation cycle.
Relying on her to inform me if our BC plan had failed somehow.
So...I think what you're saying is that you and a girl were discussing the possibility of sex. You inquired if she was using birth control, and she falsely claimed she was, and the result was that she got pregnant. Is that about it?
Pretty much, yes.
Basically equivalent to a woman saying "I can't get pregnant. This has been verified medically" as a blatant lie.
So...what legal result are you looking for?
If this is something to press charges over, criminally, or grounds for a civil suit. To document this event as well as letting her know there are consequences to hijacking someone's life