I don't have a lot to offer you by way of advice on this particular topic. My father passed in 2018 and all the infidelity issues in my marriage, some of it would happen prior to his death, but none of it would come to light until 2020 and I've often wondered how conversations with him would've gone. My mom was certainly supportive of it all, but my father was a tremendous influence in ways that I had forgotten.
My wife and I bought our second home (thought it was our forever home, but my job situation didn't cooperate) in the summer of 2014. My parents came down to see us for the first time after moving away from Nebraska to Alabama. So we got to see my parents and they got to see our new house, as they helped us by watching their grandson for the day while my wife and I coordinated all the parts of the move. My parents stayed with us for a few weeks, they really liked getting to see us and so we made plans for everyone in our family to come to my house for Thanksgiving that fall. My parents being retired, they came down to the week before and I took the whole week of Thanksgiving off to spend with them, we had all sorts of plans.
The Monday before Thanksgiving, we had just got our son off to school, my dad and I were sitting at table having breakfast and coffee when I hear a loud cry coming from our bedroom. We both rush to the bedroom to find my wife in the bathroom wailing in agony, my brother-in-law in El Salvador was on speaker, my wife's mother had just passed away. I don't even remember what we were planning to do that day, as everything was completely shot. I tried to console my wife and when I came out of the bedroom to talk to my parents, my dad looked at me and said let's go to the store, he was going to make his famous lasagna. While him and I were driving to the grocery story, he asked me about our plans for the trip to El Salvador and I told him that we agreed my wife was going by herself. I shit you not, he pumped the brakes in the middle of the road and he told me, "you are going, we are going to watch (our son's name), because if you don't, you and her are going to regret it forever. I don't care if you need to borrow the money from me to pay for the plane tickets, the two of you are going." In the end, with it being the week of Thanksgiving, we spent far too much money on travel arrangements last minute, but looking back on it now, my wife was glad that I came. She is the youngest of 8 children, 7 daughters and 1 son, 5 of the daughters lived in the USA and were married to US Citizens (aka gringos) and I was the only gringo son-in-law who made the trip, which is something her family has always kept in mind. The crazy part about all that is my wife being the youngest, we have nieces and nephews that are older than us both, so her sister's husbands were more than financially capable of paying for a trip like that and none of them came.
At the time, when it was all happening, I didn't think much about what my dad did that week. Him cooking his lasagna that day was a big deal because it meant that my wife, who was immediately in a state of mourning, didn't have to worry about cooking and her son was well fed (grandpa's lasagna was one of his favorites, a recipe I still try to copy to this day). Like I said, he passed before any of the issues within my marriage (My EA and my wife's PA) ever came to light and I've often wondered to myself what kind of disappointment and wisdom he would've shared with me/us during those difficult times.
Like I said at the outset, I don't have much advice for the situation where you are going to confront your father. Recognize that right now you have the opportunity to make things right between you two while he is still with us. It won't be the slightest bit easy, but it seems like it is very important to you and your family in recovery, so just try to show yourself and him some grace.