I don't know if this is helpful or not, but here is what I did: prior to the divorce, we had an anniversary go by. Now it's been two.
The first one was the same for me as this thread. I had no idea of OW, however, and the lies he fed me created a very thick fog, so that my blinders were still there.
About two weeks before the day of the first one, (second one had D papers filed), I wrote to him a carefully worded message.
I began by saying that I saw the dates on the calendar and what month it was. Then I mentioned that I was open to thoughts on the matter if he had any to share about the day and I left it at that.
He did reply favorably that year as he was fence-sitting (I was in the dark about this).
What we chose was to spend a few hours with DD that day and we did family things. No dinner or meals, but I put out snacks and drinks they both like. We doted on her and played games she liked and went for a walk altogether. We didn't exchange gifts or cards or speak of romantic or heavy things.
In this way, there was no pressure on either of us, as money was short, also. He came and went as he pleased and it went by without drama, but I did cry that night, FWIW. It was a lot of holding in emotion to not show him how affected I was, which I still do.
This anniversary was during divorce proceedings and no one mentioned it. I did not contact him on that day and made it a point not to...he contacted me several times, asking about DD or house things.
For this anniversary, I made an appointment and then made a nice dinner for DD and spent extra time doting on her. We did low key activities at a few places and what really helped in my mind was to keep remembering that "it's just a day on the calendar now. It's not about that anymore."
My new rule is to always make a plan on the day of some kind, so when it's looming and past and in my thoughts, I think only of the present year. It's some doing to control my thoughts, but my emotions were a lot more level this year before and after.
Such a hard thing.
A person is a person, no matter how small. -Dr. Suess
Perserverance and spirit have done wonders in all ages.