Our kids are hard work and I appreciate the occasional help we get from my family.
On top of which, you write that you do the heavy lifting in terms of emotional support, too. What is he suggesting would replace these really key aspects of your life if you moved, even for a few years?
Usually, I'm a big fan of the experience of time 'abroad' especially for children, living in another culture. Seeing the principal of 'doing things differently' operating in real life is I think one of the most useful experience children can have. My parents, well father, spent many years working abroad, with his wife and two children in tow.
However, the experience is as nothing compared to being part of a wider, loving family and having people around who can support the one person providing emotion support to your whole family.
If he wants his proposal to even be considered, the onus is surely on him to propose really well thought out, practical plans for the success of this venture. It's really not enough for him to claim that he would be 'happier' elsewhere without demonstrating his understanding of the sacrifice he would be asking.
It speaks volumes that he isn't already taking these aspects into consideration. Is he thoughtless and perhaps, yes, even selfish in other ways?
In your shoes, I would encourage him to do some analysis on what would be different for him and for each of you. What each of you would gain and equally important, each, giving up.
In the absence of something like the opportunity to earn really life changing amounts of money, by the sacrifice of your networks of friends and family, I can't see how the benefits could outweigh the costs, except perhaps just for him.
Growing up in an international community. it was very, very common for families 'sent' abroad for a couple of years to spend much of that time missing 'home' and family, only on their return to spend all their holidays coming 'back' because they missed the lifestyle (which had been so despised when they were living in it). It is so easy to blame any unhappiness on the obvious presenting difference of location when it really does tend to exist inside oneself.
There are naturally concrete advantages and disadvantages to any solution. The place to start would be for him to do the 'work' to establish the change he wants to see. So often with the right help people can be supported to understand that it is in their power 'be the change they want to see'
Whatever else you do, please don't commit to doing more than is good for the family overall, especially before he has worked out what the real problem is. An offer to spend more time over there, even investing in property at the expense of renovations to make your lives here much more comfortable may be generous. It may not be in the best interest of the family overall. Likewise, his taking time out of family life to build his own life 'abroad' without his parenting responsibilities would not, in my book, be fair on the rest of the family.
How would he make this time out up to you? What are his plans for returning the favour to you of carrying the whole load by yourself? Oh, would he perhaps not even think about that side of things ?
I'm sure many families with children have had the experience of friends from a different stage in life visiting in the expectation of recreating that carefree life only to discover life had moved on for both parties. Indeed, the really selfish ones never even spot that the people they are visiting are no longer up for late, boozy nights.
The strongest message I read from your posts, with my apologies if this is not happy reading, is that you have picked up his unhappiness as another household problem for you to solve. Does that ring any bells for you?
It might help you to step back and give him whatever space he needs to work out what the problem is and what solutions might be best for the entire family.
I would encourage him to get the 'work' on himself started and go from there. Let him come up with some proposed solutions
we can't help how we feel can we
Goodness, you are very understanding, could you be even too understanding?
Thoughts and feelings are IMO very much intertwined. The job of doing 'work' or therapy is one way to get to the bottom of those thoughts and feelings, to understand how they came to be and what we can do to accept those that suit us and discard those that 'don't work for us'. If he isn't prepared to do that work on himself then he really doesn't get to disrupt your family life for his own selfish, unexamined reasons.
Can you work on improving his life here?
Another poster somehow internalising that by dint of 'wife work' you are somehow responsible for improving his life too. Is he a child or a partner?
What is he doing to improve his life here?
You mention groups he used to enjoy attending. He is the one who needs to take steps to rebuild his life here after the pandemic.
As PP have pointed out, many of us would love to escape back to our lives when they were carefree and with much less responsibility. The secret to happiness is to be grateful for what we have and to cherish the others in our lives. To see what we can do for them not yearn for what we have lots.
I hope you manage to get some perspective on this. It's so much easier to advise someone else to stop solving everyone else's problems, than to do it for oneself.
All the very best for you and your family.