(((CDS))) I am so sorry.
Don't for a minute feel stupid and small. It is your WH that is stupid and small. You are honest, loving, and loyal and believe the best in people. Like a spouse is supposed to me.
I won't traumatize you further with details of my story, but I can say that we have many parallels thus far and it is only the tip of the iceberg for mine. But there are a few things you asked, and you said, that I feel need addressing so please know I have been in your shoes and I know what I am talking about.
When does he stop seeming filthy and tainted to you? That is hard to answer. It takes a lot of time. I think you need to reflect and think about what is your dealbreaker, what will make you decide to leave first. If you think sex with another person is your dealbreaker (and that is ok if it is)...then I think you need to prepare for D. There is no point pondering when you can kiss him again if there is no chance for the relationship to begin with.
I am worried for YOU. You have mentioned IC for him, MC etc but I don't see much in the way of therapy for YOU. IMHO, you need a therapist that specializes in trauma and if at all possible a CSAT. If you think what is happening to him is extreme, it compares nothing to what is happening to you, what has happened to you, and what will happen to you. You have basically had all the worst traumas that can happen to a person all at once. Regardless of whatever you decide about anything else , you need to make yourself and your healing the priority now. You will not be able to make the best decisions for you and your kids unless you do.
I am also concerned with your need to know the "cure" rate or relapses to decide your future. You can't cure an addiction of any kind, you can only treat it and manage it. It is a lifelong commitment, and there will always be the risk of relapse. So if that is a dealbreaker for you, that is ok too.
We could tell you all the ways that you can find his internet history on his phone and computer. You could get to 50 posts and find it out for yourself. And you are absolutely right, having to check that regularly is no way to live. But if what is a dealbreaker for you is lying, that he is continuing to lie...well, I think that ship has sailed.
I would stop all efforts on him at this point and only focus on you. What do you need to feel safe, to be able to heal, and move forward with your life? What therapy do you need, what support do you need from others? What does CDS want and need out of life?
You can always take him back later if things are not as they seem (unlikely). You can always support his recovery and healing later when you are strong enough and healed enough on your own, if you even want to. But I am telling you someone who is lying to you even now after all that has happened, is not ready to address what is broken in them, not ready to fix it. So any effort on your part for him will be wasted. He has to decide he needs to do it on his own. Now is the time to focus on you.
Keep posting. You can do this.