I think the reason Doug didn’t go through with his annulment was similar to what is troubling me now. If he was really honest with the Church, Doug risked being told our marriage could not be blessed, because the nature of his physical injury would prevent him from being married to anyone, at least in the eyes of the Church. Perhaps he didn’t want to lie to the church, any more than I would - then or now.
You may be right and you may be wrong.

Doug apparently never told you why he didn’t seek an annulment. Its okay that you two didn’t discuss “why”.
Maybe like you said he thought the Church would tell him that he couldn’t marry anyone because of his injury and didn’t want to hear that you could not be his bride in a Sacramental Marriage. Maybe not.
Keep in mind, that is one of your thoughts about why he didn’t seek an annulment followed by marriage in the Church with you. Its okay that it is only your thought and not something Doug told you.
Maybe as you said, he didn’t want to lie to the Church saying that he did not suffer from impotency. Remember that is still just your thoughts on what may have been part of his reasoning.
You could think forever and ever on why Doug choose the path he did regarding not seeking an annulment and not seeking convalidation of his marriage with you. Its okay that you didn’t have an answer from Doug while he was alive.
Its okay to not figure out if you would have kept your promise.
Lets follow the path that Doug received his annulment and you received your annulment. Then lets assume you would have joined an RCIA class and Doug would have attended with you each week.
From what you have shared with us, you and Doug would have been a couple passionately searching for all Truths about God and His Church while attending RCIA. When one of you got stuck on a difficult area of teaching, the other would be working to help. Would you have eventually joined. I think Doug would have made sure you only joined because you came to the conclusion that the Catholic Church (with all her human failings of those who make the church) is the Church founded by Jesus. I don’t think Doug would have let you joined “to keep a promise” “to make him happy”.
However, this wasn’t the journey you two took together. You had a wonderful marriage. You loved each other. You both loved God.
Now, you are still drawn for some reason to search the teachings of the Catholic Church. As I have said before, Doug could be one of the reasons you are still searching. He could be praying from Eternity for you to see the beauty in the Church. (That’s only my thought.)
You have a lot of questions. Does God grant to His priests the ability to forgive sins through the Sacrament of Confession? Does God grant to the Head of His Church on Earth (the Pope) the protection from teaching error in matters of doctrine of faith and morals through His gift of infallibility? Does He allow His Church to have some matters that are not held as infallible and have the chance to need to be changed or corrected?
Mostly, I see your heart aches over the Sacrament of Holy Matrimony. If the Church can decide that those couples unable to complete sexual unity can be permitted to receive the Sacrament of Holy Matrimony.
Keep praying. Pray for wisdom, knowledge, and understanding. I know those are all things you seek.
Peace.