You should live your M in whatever manner works for you.
You made a lot of counter-points but I think the one above sums it all up.
And I totally agree with that statement.
Well, maybe I'd say "for the two people involved in that M" to make it more clear. I might think one way but if my H thinks another, the M is done. That's why so many M crash and burn.
And of course the goal is keeping the M together...happily of course, not in misery. That's why I feel for Karen right now. She wants her M to work so bad (which I respect) but she is not finding a path to their happiness. I truly hope she does.
