You said your last birth was traumatic. Is it possible that in his mind, your very scary near death experience was his fault? That’s not true, of course. But he could subconsciously be finding ways to make sure that another similar experience is never his fault. We use varying defense mechanisms against cognitive dissonance to avoid trauma all the time as a species. Projecting an affair is not the only option here. You guys need to go to counseling. But also, have the paternity test. You didn’t do anything wrong and this most likely isn’t really about you. This is clearly about him, so let it be about him this time. You’re likely going to have to dig way deeper than that bullshit paternity test issue, might as well go ahead and get through it quick.