Thanks for the question.
It certainly is an unusual situation. If he is a widower, then he is free to marry inasmuch as that marriage has ended. That being said, the previous divorce could be problematic, however, if he is Catholic and married outside the Church, then he may well have a defacto null marriage.
He would have to consult a priest to confirm the details on that.
- That said, why are you seeking a marriage at this point in your life?
- Is it simply companionship?
I do have a friend who lost her husband and connected with a high school friend some 50 years later to go on to have a beautiful marriage later in life, so I have seen it happen but there is also a great benefit to being a single widow at this stage of your life too.
I would pray and ask the Lord what He wants of you for the next chapter in your life. That way you can finish the race in the strongest possible way.
Either way, put God first and you will find true joy.