I was going to suggest moving and not having any contact with him, but thought it could get you into more trouble.
There are people all the time that are the owners of horses or just animals in general, that have their papers yet starve or kill their animals because of neglect.
I dont think it should matter that she's not in his possesion right now. If you have a written contract that you are leasing her, maybe see if there are any loop holes you can use with that to keep her.
What I dont get is, he won't part with Possum a (please dont take offense to this) regular tb, yet Jarred, a warmblood, a Trakhner none the less, he sold.
It is great that you are keeping her until she foals. Will you get to pick the stud or will he? Are you going to get to keep the foal?
Oh, wanted to add, not sure how your lease is set up, but you should smack him with a huge bill for everything you've done with/for her. All the feeds, the blankets, the vets visits, the farrier visits, the chiro, the show entries, every single thing! Make him pay half, or all of it if need me. That might sway him to let you keep her.
(Sorry that was all over the place. It's late and my brain has been turned off)