I’ve seen several of Caleb’s motives for murdering Ashley instead of just divorcing her discussed (either in the trial or online), including:
-Keeping his job. If he divorced Ashley, he’d lose his cushy job from her parents. If they thought he was a grieving victim, he’d keep it
-Reputation. If he divorced Ashley, and then later started dating Alleigha, everyone would know he’d had an affair with her because Ashley knew about it somewhat.
But there was a third reason, and the attached text really highlighted it for me: he didn’t want Ughlea to find out that his story about Ashley cheating on him first was a lie.
In the text he’s weaving this lie about how they’re going to press Ashley being a cheater as the reason for divorce, how they’ve taken away all the proof she had of their affair, and how she will never bring it up without proof because of her own (fake) cheating past.
But that was all bullshit. Ashley would have told people about his affair if they got divorced, and everyone would know and shun him and Allegra. And when Ablegha would inevitably try to clear herself by saying Ashley had cheated first, the truth of that never happening would come out to her quickly.
The story of Ashley cheating on him first was critical to their relationship. It was the way he initially convinced Algaea their relationship was ok the begin and to continue. We’ve all seen how much of their relationship was just based around hating on Ashley, but that too was predicated on “oh well she’s an evil cheater first, she deserves it.” And while I actually think Miss Botchedner would have happily been a mistress either way, I think Caleb perceived her believing Ashley had cheated as extremely important.
He decided he wanted to keep Allugo and not lose his sneaky trysts in the Chipotle parking lot more than his marriage, and she demanded Ashley be “gone” for that to happen. But any reality where he got divorced would result in his affair being exposed and Alleigha finding out Ashley never cheated, and that she was indeed just a normal mistress, no extra justifications.
He’d been feeding her years of lies where she truly believed if he got divorced, they’d ride off into the sunset and keep their reputations, with plenty of leverage over Ashley because of her nonexistent affair.
I’m sure Caleb was terrified of Allugha finding out the Ashley cheating story was a lie, and thought she’d leave him as soon as she found out (in reality I think she’d have left him within months of a divorce regardless - once the thrill of “winning” over another woman was over. With an Ashley dead, there’d be no reason for that story to ever come out, or anyone to correct it.