My closest friend keeps inviting the woman who had an affair with my husband

Dear Delyara, My husband had an affair with a woman in our wider social circle. We separated afterward. My closest friend remained friends with both of us and with her. She says adult relationships are complicated and she refuses to “police everybody’s morality.” Last weekend, she invited us both to the same birthday dinner without warning me. I saw the woman across the restaurant and left before sitting down. My friend later said she thought enough time had passed. Two years. Apparently, she has a calendar for when betrayal becomes socially convenient. I do not expect every person I know to hate someone on my behalf. I do expect my closest friend not to surprise me with her over pasta. She says excluding the woman would mean taking sides. I told her sometimes refusing to take sides is still a side experienced by the person who was hurt. She has stopped replying. I am grieving my marriage less sharply now and beginning to realize the affair may also cost me a friendship I assumed would survive it.