So I'm going to take the liberty of moving time forward to give an idea of what the future brings.
Your S will graduate. Generally speaking, between now and then, your S is going to disentangle himself from both your H and you, on his way to graduation. That means, you are going to loose time with him.
He may or may not stay at home while he goes to college and/or begins his life as a contributor of society, working a job, having a girlfriend, a social life. Eventually, he will move away from home. Aside from what ever R he has with you, he will be gone from you.
As time progresses to that point, you will continue to avoid working through issues with your H, because you want to avoid the pain of conflict. Worst case scenario, your H leaves because the M is unfulfilling for him, which means that the two of you will separate, which means you will loose time with S.
I would think this should be motivation for you to work on the M, but right now, you would risk this future pain, for time with the least amount of pain, right now.
Lets say that is not the case, but rather, you manage to last until your S moves on. Then, you choose to D your H. Another 5 years for sure with your H will be 5 more years of pain as you suffer silently. Maybe you start to have "cravings". You start to seek the company of other men, not for sex maybe, but for emotional and other companionship. You will justify that you are not really M anyhow, that the M is dead, so you will move forward with an EA. That will conflict you, so you will rationalize more. Now, you will do your utmost to hide it, lest you dare your H or, god forbid your S, finds out. More pain.
Or, you could deny that for yourself, that human need to feel love and connected. You will dull your emotions because it will be painful. But that need will continue to be there, no matter what method you use to remove those emotions. Best case, you can become so desensitised to that need, that you basically become emotionally unavailable to anyone, including your S. Sure, you'll enjoy your time with S, but it will be emotionally unfulfilling, because you will have killed that in yourself.
Of course, lets just go through the 5 years and pretend that is not going to happen, because right now, you certainly don't feel that way. You don't see you having any need to be emotionally or physically connected with a man. You'll surrogate those needs to your S anyhow, but in a healthy way, of course.
So your S is now gone and you D your H. Right now, you will believe that it will be a pleasure. You can hardly wait to be untied from him. Almost something to look forward to. Keeping track in the calender, counting down the days. Continuing to pretend that life is good in the eyes of everyone. The truth is, another fives years with your H is another five years of history. More bonding between all of you, regardless of whether you can see it or not. Making the D even more painful. Painful for your H, painful for your S, painful for you. Never mind the financial pain, even if you are financially stable independently, there will be costs. Five more years of financial entanglement with your H that the courts will have to extract you from, when you D.
And... how are you going to rationalize filing D? Your S, whom you believe has no idea there's anything wrong, will wonder if his whole life with M parents who were working on their issues, was all a lie. If you file, he could very well blame you. Or, if he does not blame you, it may be because of the co-dependency that crept into your R with him, as you used him to meet emotional needs that should be met by a man. Certainly it will not bode well for any future R your S may have as a man with a girlfriend or a wife.
I see a lot of pain in your future, no matter how you might rationalize or justify it or hold it off.
Or, you could just step up and deal with the pain of right now, in two ways. Prevent the rest of it from even happening.
Either deal with D right now, put the M out of it's misery, a year of getting used to it and dealing with the fallout. Then, living a happy life in the future, what ever it may bring.
Or...
Deal with a bit of pain right now, and put your M back on track, so that the future of doom and gloom portrayed above, does not happen.
Of course, that horrible future will never happen, because everything you are doing right now to avoid working on the problems and making things better, will prevent the negative outcome of D in the future.
