Shouldn't be. As you know, many states including Iowa are "no fault" states, so the reason shouldn't matter. Even if it did, if he sought out the affair due to her "failure to provide companionship", it's a push in the eyes of a fair court.
You are very clear on your feelings toward cheating and cheaters. What is your stance on sexless marriages? It's a problem occurring in far more marriages than infidelity. I don't know what happened in the marriage between OP and soon-to-be-Mrs OP, and infidelity is certainly a killer, but it sounds like he was pretty miserable for a long time. He went that direction and it ultimately may have sealed it between him and her.