You have no reason to move to Portugal. You are happy where you are and you have family around you - a lovely situation to be in with retirement coming up. Make this clear to him.
It sounds as though he would not get himself sufficiently motivated to do the proper research. Tell him you do not have any wish to do this then give him a very detailed list of what you would need to know and say you will discuss it with him when he has gleaned all that information in full detail: housing in Portugal to rent, house valuation in UK, tax situation, benefits situation, health insurance and entitlements, language classes, all forms that need to be filled in, pensions, local taxes, visas etc. etc.
My bet is he will fall at this first hurdle .... do NOT take pity on him and do any of it yourself or help with it in any way!! Just carry on with your normal life.
My late OH wanted to go and live in France at one time shortly before we retired and we did look into it in detail. We both loved the country and visited frequently. We both spoke French sufficiently (I did A level and his parents were translators so he grew up steeped in languages) and I am sure we would have picked it up quickly.
But in the end after a great deal of research I had to say to him that I did not wish to do this. There were many factors that swayed me, including the presence of children and GC and likely more to come; also I had lots of musical and photography contacts (slowly built up ever many years) that brought me in freelance work which I enjoyed; I had friends and singing contacts, running a choir, which I would miss etc. etc. But there was also something less tangible - I felt that I would always feel a foreigner and never fully fit in with the subtleties of the mores and humour of another culture - I like being English and part of this culture. I also knew that the first flush of excitement for the children and GC to come for holidays with us would wear off.
My OH was both furious and heartbroken, but I also think there was a tiny bit of him that was relieved too. I knew that some of his wish to move was about his depression and he would have taken this with him I knew, but he could not see this. It was a cross he had to bear that would not go away with a geographical move. He thought it would be a magic wand cure, but I knew it would not.
How glad I am that we did not move - just a very few years later his Parkinsons Disease (which I am sure his depression was a symptom of) was diagnosed and I would have been lost without the love and support of family and close friends during his slow decline and death.
And that is another thing you need to consider. Not wishing to sound like the voice of doom, but you are both getting to late middle age and some of the next phase of your life will be characterised by physical decline - you might want to negotiate that with those you love around you.
Stand your ground.