Another example, not infidelity.
The son of a good friend of mine had a stroke when he was 4. It was a shock - he looked perfectly healthy. After several scary weeks in the PICU, he went to rehab, and he had a good (not great) recovery. He had another stroke when he was 8, this time a bad one. He was in the PICU and rehab for more than a year and was very disabled after that. At age 10, he had a stroke that killed him.
The grief my friend is experiencing is intense. A year later, it is still present in every moment of her life. When we are together, it comes like a wave, washes over her, she draws inward and howls. It's often followed by a secondary wave, which is her fear that she is a bad friend, too demanding, never giving, and that her friends will get sick of her.
Many friends do get sick of it and withdraw. They can't be around her pain. They want it to pass quickly, to say platitudes, for her to find religion or whatever, to talk about mundane things, or to keep it in the appropriate time and place. There are many ways to signal to someone directly or indirectly that you can't handle what they are experiencing.
I've often prayed to God that I would be able to use all of the skills and knowledge that I've acquired through infidelity to some good purpose (apart from my husband and family), and being present for her during her pain is one thing that has been positive. I know how to be with her, when to talk and when not to, not to signal discomfort when she is howling. Mostly I quietly pray. When she is coming out of it, I know how to talk to her about her other worries, point out to her that she asks about how I'm doing after she has processed a teaspoon from her mountain of pain, and thank her for letting me be a witness with her and giving me the opportunity to be with her. She knows about my infidelity and I tell her that I'm happy for the peaceful moments of life, but that being able to be with her during that time is a gift to me, not something I'm begrudgingly doing for her and waiting for it to end.
The analogy to infidelity is, of course, that I am the one who killed her child, and yet she wants me to comfort her.
When your husband has pain, he needs someone there to witness so he is not alone, and he needs to know that you will not try to divert, hurry, minimize, or otherwise manage him. You might find gratitude for the opportunity to simply be with him and patience to know that even though it doesn't look like it's helping him, it is. And you can be alert to things that he finds helpful. My friend worries that her son was afraid during the last moments of his life, because he knew what was happening to him and that it was bad. I've found things to say about that which she finds comforting (and I've learned through gentle trial and error what is not helpful). So I repeat those things, gently, and the repetition of those images and phrases can help her to replace her fearful ones. So you can be alert to the pieces of truth (it must be truth) that he finds helpful during those times, and never get tired of repeating it.