This is a tough one because neither of you are being unreasonable, you just want totally different things.
I probably understand your point more because I’ve lived abroad for a long time and although I’m now back in the UK for the foreseeable, I would certainly move abroad again under the right circumstances.
However, one of the many problems in my previous relationship was that my ex had spent his entire life in our hometown and despite saying at the start of our relationship, he would “never say never” to moving one day, it became very clear after a while, that he had never had any intention of moving about more than 30 minutes from here - even that would have been a battle.
Again, neither view is right or wrong, it’s just different, but it’s one of those things in a relationship where you can’t really compromise.
You say you’ve been married for 30 years. Is this the first time that living abroad (not even just Australia to be with your children) has come up? If your DH has always been clear that he wouldn’t move, that’s fair enough and should have been something you decided at the time whether you could accept that or not, but if he’s said for years that he would move and is now suddenly moving the goalposts, that’s a bit different.