Ask him to find out what health care costs in Portugal, how you would be placed if one or other of you had to move into a care home later on, and whether you will need to pay tax both in Portugal and in your native country.
Finally, whether he wants to be buried in Portugal or not and whether you will both have to re-write your wills to ensure that they are valid in botoh countries.
In Spain an estimate from a tradesman is only binding with regards to cost if it has been notarilized by the public notary, which of course requires you to pay a fee. I do not know if the same applies in Portugal, but it may well.
Finally, you both need to learn the language - English is not spoken automatically by everyone of our ages, or even by professionals (doctors, lawyers, undertakers etc,)
So take a long hard look at the practicalities and make him do so too, before considering a move.
Might a compromise be possible? Spend part of the year in Portugal, part at home?