We have this from different angle. When my in-laws moved house 16 years ago they moved further away from us, not much further but a far more difficult drive. At the time I'd already had to retire due to ill health and disability and my husband was, and still is, my carer, in addition to working, but they wanted to live in a certain area so moved there, making visiting difficult. 40 miles can be a very long journey when one of you is ill and in pain, believe me. Anyway they got older, his mum had to go into care but visiting was difficult, then she died and we're now left with an 86yr old Dad we can't visit easily, at moment it's not even possible to drive there to stand outside and wave. Had they chosen to move closer to us all those years ago how much easier our lives would be and my FIL would be visited far more regularly by his family. We and our adult children and their families all live within a 5 mile radius, it's so much easier to visit each other and even at the moment if someone is in difficulty re shopping we can help each other out occasionally. If my FIL was nearby it would really be to his benefit, I think they forgot they'd get old and possibly disabled and would need their son's help more over the years, sadly it was their choice and my DH has to put restrictions on visiting etc as we aren't getting younger. I'm now only 5 years younger than MIL was when they moved there plus I have lot of problems that mean I rarely go out, my husband wants to spend time with me, not travelling on motorways and being away from home for 3hrs minimum, usually more like 6 hrs, every time he goes to see his Dad, if only they'd moved closer to us how different it could be.
If your son is unlikely to move from that area I'd suggest trying to discuss the benefits of the move you so desire in hopes that your husband will gradually come round to the idea. He might do, if he doesn't then there's not really much you can do about it. Good luck.