Don't get hung up on diagnosing his disease (dis ease). He is not at ease with himself or his life. He doesn't know what will help. He has flashes of happiness and then they vanish before he can solidify an answer.
Mlc or not, DB teaches excellent practical techniques for managing yourself in this time. DB may or may not alter the outcome of a MLCer. It does not say it can. But it can guide you to calmer contacts and more stability in your own life. DB says to take care of yourself. MLC says to let them flounder in their own confusion. It is not out of spite. It is the only way they can process this life stage transition they are caught up in.
Maybe your H is not full blown MLC, but just a WAH at mid life. They all follow such a similar script it can be impossible to separate the two. If thinking he is MLC helps you understand your options then come to your own conclusion based on his childhood, his perception of where he is in his career, etc.
He says sell house and you try, he is not ready. He says get the D and you start, then he is not ready. Let me share what those observing MLC here for a while will tell you. Stop trying to make him happy. Stop now. You can't, you won't, and it will destroy you.
You can do things to avoid conflict. This is the most one can usually hope for in surviving mlc. If he says he wants to sell the house you should decide that he is saying this to see how it sounds to himself. He is trying to decide if that is what he wants. If it is, the best way to find out is sit back and see if he sells the house. One common trait of a MLCer is they run out of gas. They don't complete what they start in things of this nature. A true full blown WAH seems to already have his plan in hand and a roadmap out of there. MLCers are confused by their very existence. They are supercharged with depression, guilt, and low self esteem. They are trapped at a crossroads and you can not help them make these decisions.
Do you want to sell the house, or get a D to make your life simpler? If you do, maybe you just aren't prepared to ride out this storm, or you may also be in your own mlc. That is not just a joke. It is not unusual for mlc in one spouse to cause a crisis in the other. The degree of turmoil depends on childhood issues, self esteem, and a comfortable relationship with mortality.
When a MLCer wants a D, you can avoid challenging them by stating that you understand why they feel the M is broken. You can state that you don't want it to end but that if it is dead and gone then you will not fight them over this.
That gives them the control and validation they think they want. They may not make a move beyond that. Getting what they want confuses them. This could be why you keep trying to appease him and feeling confused when it fails. Stop trying to do that. Practice "agreeing and validating" without promising to take any action what so ever. Let him run out of gas in his own time and at his own pace.
Your focus must be on keeping your tank full. Do things for yourself. Do things that make you happy. Do NOT look to him for your happiness. He has none to share. Do not be surprised to find out he is considering an OW at some point. MLCers try anything and everything to make themselves happy. OP have nothing much to do with this except that we become destroyed in learning we are replaced by another. Again, that is more our fault for losing perspective than theirs for experiencing and exhibiting all the symptoms of mlc.
I also state that mlc is not a get out of jail free card. Forgiving a person does not require forgeting their actions. The two are separate. Knowing they did not do something just to hurt you allows you to forgive them in some ways. Knowing they made decisions that hurt you make it hard to trust and time alone will heal that wound. The scar will stay and you will remember to be watchful in the future.
There are no rules for how to keep mlc from destoying a M. There are books and ideas on how to try and survive it yourself even if the M doesn't. That must be your focus.
