According to what you wrote, you probably need to make your personal safety the most important thing right now. And let this direct all of your steps.
1. Probably the best & safest thing for you to do is move out now in a way where she and anyone she knows will not know where you moved to.
For now just get a temporary place to stay and if you have a lot of stuff, find somewhere safe to store it for now.
When you leave take all the documents that show you paid for the land, paid to get the house built and that you have a usufruct. (All bank transfer documents, receipts etc) And take every thing else that is important to you and every thing that you can show you paid for, and take all these at the same time.
It will probably be best to move when she is not there.
2. Find a recommended English speaking lawyer that you can understand.
Getting a lawyer should show her that you are not just going to give her everything.
Someone earlier said they know of a lawyer that has helped them with a similar situation.
3A. Either have your English speaking lawyer contact her and try to get a settlement worked out, with her either paying you for your half of the house or agreeing to sell it with the lawyer overseeing the sell.
And it will be best to sell the house as fast as you can, even at a low price so that you can get what you can and get on with your life.
Or
3B. Show your lawyer all the documents, receipts, and the usufruct, and ask them do these documents show that you are the owner of the house?
If yes, ask the lawyer if there is some type of sign that can be put on all the doors of the house that says in Thai – Everyone must receive permission from your lawyer or yourself before they enter the property.
If you can do this, ask the lawyer to get the police or someone they know to put these legal notices up and send you pictures.
Then ask the lawyer that even though you have moved out, can you legally do anything you want with the house?
If yes, there may be a scrap/recycle businesses in your area that will pay you some money for the roof materials, all the steal and even pay you to be able to destroy the house, so they can sell the concrete and brick rubble for land fill.
If you cannot find a scrap/recycle businesses in your area that will pay you, you could probably find someone you can pay to remove the house.
Remember your personal safety is always your most important thing.