The first time Hermione ever confronted Antonin about his affair with Andromeda Tonks had not gone well. Allowing the cheating to happen was one thing. Talking about it was something completely different. They had been married for five years, but his wife had known there was something going on for a lot longer than that. How she knew was unclear. Maybe it was one of those secrets that everyone knows about and no one can remember where they first heard it. Again, it wasn't as if she could exactly judge his actions. She was guilty of plenty of unfaithfulness herself. It wasn't as if they wanted to get married in the first place. At least she didn't. Antonin's motivations were always suspect in her mind.