So yeah, sorta. She's an average 40 year old lady. Thing is her husband is average too. Don't know what this hot 25 year old sees in him at all (he's overweight doesn't have a good job, etc). So I get where you're coming from, yes, she's let herself go a bit but he has too. So it's not a thing of one partner letting themselves go per se. Hell, most good looking 40 year old women aren't going to stand up to an average 25 year old.
As to the affectionate thing, apparently they had a lot of sex until she found out about his affair. I can't speak to the kind of sex, if it was good or not, but apparently frequency wasn't the issue.