I don't think you need a visa for that. Lots of Australians work 2 weeks on 2 weeks off Thailand vs Oil&gas or the mines etc you get 30 days on arrival. As long as you're not working here you are good :)
You need to show your gf has reason to return to Thailand, Job, dependents, assets. Your circumstances are not so relevant, just maybe a letter / statement saying she will stay with you.
Bringing a dependent to the UK now requires something near to a 30k a year in come and will tie again soon. UK government has an issue with us bringing our loved ones to the UK apparently. ...google is better than Facebook for facts