I think that all the vitriol about what a bastard he is might be a little OTT and could have a negative impact in terms of validating the OP’s self-esteem; as in “how could I be so stupid to not see him for what he is?” and “how worthless am I that he dropped this on me when I am so vulnerable?”. Sometimes people get caught up in the collateral damage by association.
I know people in the kink space. Some of them absolutely hate themselves for what they sometimes see as perversions, flaws in themselves. I’ve known people who try to push it away for years and years, until a trigger brings it out. I suspect that the OH is suddenly feeling ‘trapped’ due to the pg, and that this created the crisis.
Not that any of the above actually helps the OP. Fact remains that she has been blindsided and deceived; no-one should enter committed relationships whilst in disguise (as he did), and it is even worse when a known imbalance in sexual compatibility is ignored (by him), rather than discussed AT THE OUTSET with the unsuspecting partner. Both are cowardly and destructive, and have sown the seeds.
OP: you could not have foreseen this, the deception is what is unforgivable, and the person he has laid out in front of you now is the ‘authentic’ him. You are not to blame at all for the situation - in fact he probably tried to ‘fix’ himself because he wanted to be worthy of you, because of the high regard he held for you. Not that any of it matters.
Your sexual incompatibility (and his dishonesty) are probably impossible to overcome. I have known partners of kinksters try to explore the scene itself, to support their partner, and usually they end up feeling wretched and used.
My suggestion?
(1) If all thoughts of dom/sub, BDSM, kink or whatever are so repulsed, then the marriage is over;
(2) if it is a case of “🤷♀️ WTF is that all about?” then maybe a trip to a club/dungeon might show if the OP could ever even begin to accept this space (I imagine that unlikely). But even then, I think the marriage is pretty much dead anyway because of the deceit.
it isn’t a case of him changing: it’s possible of course, but (vanishingly) unlikely.
Your challenge isn’t about what to do with him, it’s about your pg. if you carry on with pg then he may remain in your life forever, arguing, trying to control from a distance, have joint custody, etc, etc. Factor that in when making your decision. Is he a good dad to the kids he already has? Would his parenting as an ‘ex’ be good enough for what you want for your child? Measure him on the person he is, not the one you thought you had.
good luck.