EC just capture what you can... your H is going to therapy now and is diagnosed with Sch. so it won't be hard to get some leverage...
It is VERY HARD to prove to a court that your H has an addiction to a romantic fantasy... that's new ground on the family therapy front... hollywood has been celebrating infidelity for decades and most novels and other media just paint infidleity as a tragic romance not an addiction.. teh addiction thing is NEW ground...
But your H is already diagnosed with problems so you likely won't need to go that route...
Multiple personalities? DId you READ shirley glass' "Not Just Friends?"
She has a section int here called "Leading the Double Life"
You can't have a secret sexual affair with someone and NOT live two lives...
Keep showing MIL texts from him.. If you want to hold out for another week while planning then keep collecting info and showing it to MIL... if its waking HER up and his SISTER up to how ILL he is right now that's all the better...
You need their support, not just passive nods in the corner when he isnt' home and then they HIDE from him like he's some BULLY...
DOn't let him bully you or his family.. expose to his family those texts and collect more if you think its waking them up ...
