Why bother texting pretending to be anything?
You know what he is. Who gives a shiny shit what the details of his latest tiresome, predictable, loserville cheaty-times are?
You'd be far far better off planning what YOU want to do next, for YOU, what would make YOU happy, how to get the future YOU want.
He honestly is an absolute waste of any headspace.
Start thinking finances.
GCSEs will be done soon...
Your business, or both of you?
Joint account, joint savings? Get details of his holdings, account, pension. Get access to what you can and copy docs.
What's the situation with the house?
Get your ducks in a row and leave the little shit.
Oh, and if you do any texting, just reply to her:
'Love, save it for someone who gives a shit. You're the fourth one since November. All I can say is that I'm getting more grateful to you and the others every time this happens (and he's once again too thick to cover his tracks) - there's nothing like hearing it from the horse's mouth. Remember, that was the last message you were going to reply to, so I don't expect to hear any more nonsense from you. All best, X'