It really has nothing to do with trust

I'm sorry but "trust" in the way you're talking about isn't what this is about. Like I said, people who don't have issues in life don't seem to understand. The man wants to know if a kid is his. He's doubtful and scared and worried. You don't just say "Can't you trust me!" and magically it all goes away and he's okay now and 100% obviously because he trusts her then it's his kid for sure. You do get that right?

Life doesn't and shouldn't be left up to trust like that anyways, it doesn't even make sense in my opinion. I trust my SO with my life, but who knows what I'll feel a year, two, three, 10 years from now. What if my kids look nothing like me, act nothing like me, seem nothing like me. What if doubt creeps in all those years later? What if the depression and anxiety creeps back in and I start to resent my kids, or my wife....

Why leave that up to what I feel right now? Loving my SO doesn't mean I shouldn't protect myself from future doubt and issue.

I know my SO would take care of me if I was dying. This doesn't mean I ignore setting up something for hospital stays or clinics that could take care of me instead, in case it's too much for her or she's unable for some reason. Trusting that someone would do something, doesn't make it reality. My trust for her has nothing to do with setting those things up.

I assume I'll be downvoted because this subreddit is kind of insane sometimes. It's either the wife is a slut, the guy is crazy, everyone is should have blind faith in all aspects of life, and if they don't, clearly the whole family needs to get down to therapy and work it all out. But also, make sure you break up first, because that's a "flag."

Not everyone is caught up in today and this moment. I'm not. I know that the future could hold worse days for me, days where I no longer can rely on the "trust" I feel in the way you mean it. That's just not how the human brain works, especially when it's scared, depressed, and doubtful about life.

If you want a more clear TLDR style answer. Trusting your SO has nothing to do with trusting yourself, and if you honestly think that you can trust your future self to be perfect, or believe that trust in general is something you can walk around relying on, I think you're delusional. Relationships are built on trust, life doesn't take this into account, and trust isn't a magical unbreakable bond, so I don't rely on it. This doesn't mean I don't trust my SO, and the OPs husband isn't being untrusting, he's being human. It's his right to know if his kids are his 100%, not to just "trust" it.