Most likely husband has something going on as well. But maybe not. Honestly the Wife and Husband was a mismatch from the start. Dude already old, and the wife is young and he was her first, and she has a sex drive. They should honestly respectfully divorce.
She's already technically cheated but nothing's been penetrative. It would be best for the three of them (incl hubby) if they divorced before that. If she gets caught cheating things could get nasty.
She's far from happy in the marriage and it seems that to the hubby she's more like a maid than a wife. The downside for Makato is that Aki doesn't make enough as a mangaka to support them both and she would have to work. It's possible she could get a temporary teaching assignment but more likely she'd end up working at a konbini or serving at a restaurant or izakaya. Those knockers would make her (mature) eye candy for half-drunk patrons.
We really don't know a damn thing about the husband except he's in sales and it may be education related. We also know that he's passive in sex, practicing what is essentially the male-equivalent of the starfish position. He seems to find sex annoying, exactly opposite of Makato.