I've gone through one college graduation of our oldest, and two high school graduations. My ex was at all three. For the last two, he brought his new (20 yrs younger) wife. She was not an OW. She was someone he met, and has never been around our children.
I am completely polite to them. I never sat with them, and I made sure I had a "friend" with me...along with all our other children.
Give it time. For me, after a bit, it was very easy. I discovered his new wife hates me (and the kids). Shes from another country and I think was expecting an old Russian 40 something yr old when she met me. Nah, not exactly. That gave me so much relief. I felt like it empowered me.
What I see now is my ex is the one who's sad and regrets the life he's carved for himself. I think he sees who he lost, in me, and he is far more miserable than I am now.
Maybe it's wrong, but I do get some satisfaction in all of that.