Question on seperation... Please answer if you can..?

My dad has been with a a woman for about 15 years, But he is now very unhappy in the relationship. He wanted to leave a few years ago but his partner got a brain tumour. She is better now, although she is classed as disabled. They never married, But now he wants to leave, He's worried she will get the house because of her disabillity. I personally thought that they would both halve their assetts and be done with it. But apparently if he leaves her, She will get the house because of her disabillity. Anybody who has any experiance on this, Or knows what he needs to do in this situation please let me know, Any insights Are greatly appreciated. Ideally he just wants a clean break, Half each of everything and so on. Thankyou :)