dh keeps doing something during sex which I don't like. I ask him not to and after a few minutes he does it anyway.
He apologized after and said he won't do it again (he says this everytime) and now he can't understand why I'm still pissed off.
In what way does it not fit? What bit is different or missing? Facts don't alter just because another person wants them to. And while her husband may actually just not really understand the seriousness of what he's doing, because we have, as several comments indicate, a culture that almost permits men to do this to women they've had a sexual relationship with, the reality is plain: his actions are squarely and clearly under the definition of the crime. If she reported and he confirmed, he'd be a slam dunk case. So how, if an honest admission of what he's been doing would earn him a conviction, can it not be assault? Do you think a crime is dependent on the victim's opinion rather than the definition? Seriously? Because it would be horribly disturbing if it worked the other way.
I'm genuinely baffled that people can read that, and then read the very clear and simple definition of the crime (inserting anything into another's anus, without a reasonable belief that they are consenting to that insertion) and argue that it doesn't fit this situation, and his doing precisely what the statute describes doesn't matter for X Y or Z reason. Crimes aren't interpreted like that. They aren't that flexible. Certainty is pretty important, when dealing with people's liberty and future life chances.
The OP doesn't see what he is doing as assault. Probably, nor does he. But the definition is a legal and not a personal one. It doesn't alter with their opinions. It's a set of circumstances which fits this situation exactly, precisely, completely. That isn't something you can just hand-wave away, because it isn't down to the individual to decide if they personally feel in their waters whether something is criminal. It's down to the statute. The point is that she has no intention of making a complaint, but that doesn't stop the action itself being criminal. It just... is.