First, the back and forth lasts a lot longer than anyone wants it to. WRT behavior, I was on board for R from d-day on, but anger at the unjustness of the situation reared its head again and again.
To R, you've got to accept that this is just another area of life in which justness and R are incompatible. We can have one or the other, but not both, and certainly not both simultaneously.
Have faith in yourself to come down on one side or the other in due time.
*****
I'm usually on the side of sharing feelings, but with this, at a year and a half out, not so much, maybe. If you think it's too early to hold back expressing anger, you might be right. If you can tell your H that you're having trouble with your decision, that may help you more than expressing anger.
Do you see your problem as your own to solve? I do. I think this problem that you describe is a 'simple' matter of choosing one path or another - justice vs desire to stay together. I understand that you are a victim of your H's infidelity, as all BSes are, but the fact is that we have to deal with the feelings of being betrayed, and at some point we need to decide to let the feelings go in order to heal. Is this the time for you? Maybe - you're raising this issue, and that may mean you are ready. OTOH, maybe you're not ready yet.
If you still the issue as anger, disgust, desire to hurt your WS - all of which are normal up to a point - what's the positive outcome of sharing that? If you don't see a positive outcome, hold it in until you do. If you do see a positive outcome, go for it.
Whatever you do, do your best to put fear aside. If fear is telling you not say what you want to say, it's probably best to say it. If fear is telling you to say something, it's probably best not to say it.
*****
Bottom line: I guess I think you are at a crossroad, and I think it's the justice vs. desire to rebuild with one's WS.
Whichever way you turn, I believe you'll get to similar crossroads in the future. You have to make a choice now, but you'll be faced with the same choice - justice vs desire - again and again in the future.
It's burdensome, to be sure. It's also means you'll have many opportunities to make good choices for yourself, even if you blow one or 2 of those opportunities along the way.