Many years ago my dad went for his annual account review with the bank manager, back in the days when bank managers knew their customers individually and were the literal managers of their branch. He gave my father advice on his money, at which point my father said, "You're very good at this, your own finances must be in great shape"

The manager replied, "God no, I'm great with other people's money but I'm awful with my own."

It appears to be a truism that you don't have to have good personal behaviour to give good advice.

The fact that Sabrina had strong enough suspicions to broach the subject suggests that it was apparent, eventually.

I disagree, I think the dynamic has nothing wrong in it at all, but I think the fact that OP didn't mention any of this to Sabrina was definitely a FU, and the fact that the first statement mentioned is "How could you keep this a secret from me?” succinctly sums up the betrayal.

You have any number of reasons to blame for why you did what you did. You literally have no-one to blame but yourself if you don't reach out and explain to him what was happening to give him the chance to understand and forgive you for what was out of your control. Don't be that person that disappears a whole possibility of their life through anxiety and fear. Grasp that hope that he'll understand and even if he doesn't, it will be because he doesn't want to rather than because he doesn't know.

I would say that he has exhausted your trust in him, which is a glass support that once broken cannot easily be reconstructed. I presume you've pointed out to him that he has no revealed that your boundaries are obstructions to be worked around, rather than actual boundaries? Because his dishonesty is exactly that, a refusal to accept a boundary and see it as an obstruction that needs action to circumvent.

Look, there are some people who enjoy this kind of thing, and there are some that don't. The issue here is he's one of the ones that does, and on finding out you are one that doesn't, he's trying to force you to do something you find repellent regardless of how you feel about it. He has already taken your non-refusal as consent and gone ahead with the arrangement. That's partly on you for not, once again, refusing him, but almost entirely on him for just not accepting a no at the first expression of it. He thinks you can be persuaded, doesn't care that you don't really want to, and is forging ahead. He almost certainly will bring this up again because he's got the idea, from porn or just his own fetishism, that you can be brought around to his way of thinking.

As you say, the real issue is that he won't admit that actually making this happen is a priority for him, and you saying no is a negotiable. You can't trust him not to arrange this again, you can't trust him to not keep pushing it. He HAS to accept that this is never going to happen, and without that you have no marriage future.

There's no avoiding the science of DNA tests. He gets proof, he knows where he stands. If she consistently refuses to allow him a test then that's an answer in itself.