However, JA kept denying the tires and afaik TA had no proof it was her. Now the pedo pamphlets she claimed to have sent him, that could easily have been the last straw(can you imagine if someone sent you something like that and said they were going to go public with claims of it??!) and from the letter she followed up with I think she realized that. Plus whatever that scamming remark was about(ie. if she had hacked into his bank account, or they had actually had had a joint one, perhaps she'd emptied and closed it/them out, heck maybe she somehow got a payout for the car and left him to finish the payments for it) and then there was the issue of having stolen his journals too, something that from his book excerpts sounded very important to him.
Surely TA had limits on what he would take before writing her off and I honestly don't think sex was enough of a payoff for what she had put him through by then for him to let it go, not even for one last time.