None of this is happening in a vacuum.
Sometimes, when people are under intense stress, they self-destruct or do things they wouldn't normally do. Some people use booze, drugs, food, their credit cards, and some people use sex. IMHO, that's what makes the analysis of Terri's behavior so difficult -- is her sexting Michael Cook reflective of her true personality and does that have any real bearing on Kyron's disappearance, or is it reflective of an extremely bad choice when dealing with unusual and extraordinary stress?
She could've been sexting because she's glad Kyron's gone. She murdered him, and she's moving on.
She could've been sexting because she's glad Kyron's gone, but she didn't murder him.
She could've been sexting because she has unhealthy views about sex.
She could've been sexting because she enjoys male attention.
She could've been sexting because she has unhealthy views about sex, her husband left her, took the baby, filed for divorce and a restraining order, and Michael Cook preyed on an emotionally vulnerable woman.
She could've been sexting because Kyron was missing and sex is what she uses to distract herself from things she doesn't want to think about.
It could be all, some, a combination of, or none of these things. To apply a simplistic answer to a complex situation is a mistake, IMHO.
TY for sharing your logic and common sense here
All JMO