He does have to. Someone accuses you of banging his wife, you either clearly say that you aren't, or your silence will speak volumes.
And what's happening here is that Namor is saying that yes, they do fuck sometimes, but it's just an escape from her frustrations to her, and never let's it become emotional attachment.
This is literally what Bendis was writing. Consider it canon or don't but that's what he was doing.