The really hard truth in all of this is whilst you've been loving him and prioritising him, he feels entitled to exploit, manipulate and hurt you to get exactly what he wants. Up to and including violence. He fundamentally thinks that treating you that way is justified, to serve his own purposes. Because you don't really matter. For him, you exist only to serve his own purposes. Your life, your feelings, your dreams are only a consideration so far as they can be manipulated. He doesn't care if he lies to you, hurts you, humiliates you, frightens you. You might as well be an object. If he's attached to you, it's the way people are attached to a possession.
So it doesn't really matter if he actually only wants to have sex with men, or why.
Exploiting you reproductively to give him children is just a part of the overall picture of him exploiting you more generally to give him whatever he wants.
It's time to put a stop to it. You don't need to analyse the reasons - the reason is simple: because it suits him, because he feels entitled to do it, because he doesn't care about the impact on you beyond how it affects him.
You'd be better off seeing this "breakdown" as an overflowing of his selfishness. He's no longer able to "live the lie" that he cares about you and his children, but wants to frame it as something more sympathetic. That's what this is.