It's the loss of our joint lives and memories.

My experience was totally different. Paid off the house early in the relationship. No kids (together) which gave us time for each other. Lots of vacations and life changes and personal growth. I was retired and she was about to finally say enough of work. Both had filled our bucket lists to overflowing. What was missing was the future plans and the hope of a better life. Actually, it was a good time to go and, from her actions, she appreciated this more than I. Still, some of us (myself included) have got to learn to more fully appreciate what we had and hope another bond comes along.

I have lost two spouses and have gone on each time to a new relationship. It is my experience that each relationship is different and has its own "vibe". It is the melding of two unique persons into one shared existence ... and there are lots of ways to share it, too. In addition, you are changing yourself as time goes on. So it is not a particular problem to attain intimacy with a new partner if that's what you value.

That said, I do understand (1) the ideal of sharing an entire life with one other person, which was very much my value going into my adult life and first relationship, and (2) while love is not a zero sum game and you can always enlarge your circle of love, it is extra work to know and be known by additional person(s) and to have some kind of orderly story arc constantly interrupted by tragedy and new relationships.

As such, I am quite certain there is no 4th marriage in my future, should something happen to #3, and since I am my current wife's #3 it happens that she has expressed the same thought. It is not that we don't love each other or that we are "settling" in some way but beyond a certain point it just makes life too complicated in between your ears. In addition, hopefully as you get older you get wiser and more centered and confident and you lose the FOMO (fear of missing out) that drives you to the next relationship. You can be content with less. And particularly if you're an introvert, you can enjoy the upsides of living by your own lights.

Everyone has to thread that needle in their own way, but my thought about your musing is that you should in no way assume that no one could possibly love you "anyway" just because they don't have a memory of your salad days. It needn't be awkward. Remember that other people operate under the same constraints you do ... they are older, less energetic, less flexible, etc. They are just as in need and just as limited as you see yourself being. You aren't unique in that regard.

each person's experience of loss is unique but you certainly summed up my experience too - thanks