Sometimes we need to act on what we know, and sometimes even on what is probable.
For example: If you are walking along a dark area of town and hear what might be a gunshot... Would you walk towards the sound to discover the origin, or would you decide to walk a bit faster towards safety? Maybe even run?
Could be a firecracker. Or a tire blowing. Or a muffler. Or a nail-gun. Or somebody dropped something heavy. Could even be someone shooting at rats, or target-practice. Why assume it’s a gunshot and that it’s being fired in a malignant purpose? Why do you feel a need to go towards safety? Out of the situation? You don’t have the truth, but you have a sense that you might be in danger. That’s enough to act on. It makes more sense than to search for the cause of the noise and maybe realize the "truth" a second before a bullet enters your brain.
To me it sounds like you are in a comparable situation.
I don’t know if your husband is actively cheating right now. But based on what you share, his attitude is all that it’s OK, it’s not so bad, it’s not a serious issue, that it’s normal, that it’s accepted, that it’s something he needs to do because he cant get it all from you, and that it’s something he’s been doing forever and hasn’t really committed to not doing it...
To me – that’s a lot of sounds like gunshots...
If this marriage is to survive your husband needs to make some major and serious attitude changes. Based on your last post, he’s not going to do that as-is. He knows that for now his cost for continuing his actions is simply to wait and see. After all – it’s only costing him that you sleep in a separate room and occasional hard talks where he controls what he divulges. He knows he can refuse to tell the truth, that he can refuse MC... that the "worst case" scenario from him (as he sees it) is that you sleep in a separate room. Guess he still gets free laundry and dinner. He can spend the evenings and nights on Tinder or watching porn or whatever.
Nothing will change until you decide that whatever he’s offering isn’t enough, and you want something else. Nothing will change until he sees he no longer controls what he shared and does, and wants to make the required changes. That MIGHT happen when he realizes you are leaving. Or it might not. Either way, you will be out of infidelity – with or without him.
"If, therefore, any be unhappy, let him remember that he is unhappy by reason of himself alone." Epictetus