Here is my rule of thumb for living your best life. Avoid any adult whose moods are bad enough to require your input to manage them.
The only person who can possibly change this behaviour is the sulker themselves. They are choosing not to change it. Why should you even try to dance around them ?
It's just a form of control. Don't join in, don't play the game. Whatever you do, don't marry them.
Why on earth would you even want to marry them?
Blowing up a happy healthy relationship for human flaw and frailty cannot be the first option
Once you see that it's very deliberate behaviour designed to control you and keep you in your place , I really hope that you can see this differently. The onus is not on you to fix his human frailty, it is for him to stop this cowardly behaviour.
You can quite straightforwardly explain that you won't put up with it. The way to avoid blowing up the relationship is for him to stop it.
He is very unlikely to stop because it is behaviour which is really working for him. It's you that feel uncomfortable. You are are trying to work out how to fix it. He is doing fine with it
That l's why I suggest that you put the wedding plans on hold while you work out together whether you truly will accept his control in this way. Let's face it, it isn't going to get better while it's so useful for him.
I wonder if he feels i dismiss his feelings by wanting to make up so quickly
Oh, this is so sad. You have had seven years of being dragged down so that you jump to the conclusion that somehow his behaviour is somehow your fault?
My earnest wish for you is that you get to see an example of a healthy relationship where differences can be examined and explored and a compromise reached.
That is a million miles away from one partner sulking and the other dancing round them trying to make it better.
You can't. You really, really cannot. Only he can make the change. He would need some reason to change his behaviour because it is working out so well for him.
Even to the extend that you are questioning yourself, wondering what you are doing wrong or not doing. Even if he doesn't do it deliberately or consciously, the effect is still that you are trying to solve something that he and only he can do.