I think there's more to the story here. Where in Thailand before going back to the UK? How long were you gone? Maybe she found something you didn't want her to see? Maybe her friends told her Thailand is an adult Funland? Maybe she cheated on you and decided she wants the other person?
From my experience, once a woman makes up her mind to leave you, 99% of the time, it will be very hard to change her mind.
You need to find a good divorce lawyer to protect yourself.