... to think a lot of middle aged couples stay married for convenience

[HofstadtersLaw]

That's certainly my own case. We've drifted apart over many years and live very different lives. I've met someone else, a good friend, but that is all for now. I'd like to change that so have some big decisions in the coming weeks for me.

DSis is in an unhappy marriage too. Feeling unloved, not appreciated, no sex, etc. She's decided to wait things out until youngest starts work or goes to college.

My best friend has no kids, and happy staying in her marriage for financial and a few other reasons.

Is it just me and people I know?

I divorced at 36, and again at 41. Never again. But I wasn’t financially supported by my exes.
Two of my friends no longer want to be with their husbands, but don’t want to go through dividing things up, and working full time to survive. Nor do they want to be alone.
To each their own, wouldn’t suit me, but it’s their choice.

I'm sure plenty of couples should probably split but I doubt they are together just for convenience. As others have said, it's more likely because of financial consequences or constraints, children, fear of the unknown.

We celebrated our 35th anniversary yesterday and have been together almost 40yrs. We were together 20yrs before having children and our boys are now getting ready to spread their wings. Without doubt, the hardest times in our marriage were when the boys were small. Working full time, skint, huge mortgage, children, they all put a strain on a relationship.

Now we are retired and are very happily 'plodding along'. Life is calm and chilled. We both have hobbies which give us plenty of alone time, but behind closed doors we are still feisty, have massive discussions/debates/arguments about everything under the sun and a great sex life.

The point is that only the people in the relationship know why they are still there and, for some, convenience might be what they need or want.

I have two friends who are open that the reason they have stayed (and both left or separated for short times) is financial and functional- they don't fancy being poorer single parents doing everything for three kids all the time without the money and physical support of another parent to drive them around, do the dinner and so forth. One hasn't worked for many years, she would be on benefits, she doesn't fancy that and has a lovely life, so the fact her husband is emotionally dysfunctional is the price to be paid. The other likes her husband but nearly left him. I think it's fine to decide that life would be harder separated and act accordingly, not everyone conforms to the endless love match of Disney.

I also think some marriages come around again to be better when you are older, especially after menopause, I've seen that in my own family.

I don't think you should stay for the kids, my parents are much better apart but I think it's ok to make decisions about how you want to live and if you aren't unhappy and it's better for you financially and support-wise to stay in a marriage, then that's fine too, and not always a bad decision.