The government of Thailand is right now (2023) studying the possibility to legalize same-sex unions, what is commonly known as “gay marriage”. It is not adopted yet on the day that we are writing this text but just a proposition. The new elected government has promised to move forward in the next 100 days.

On 14 May 2023, a new government was elected and they also proposed to legalized it but nobody know when. in June 2023, probably the future prime minister of Thailand, Pita Limjaroenrat promised same sex marriage. See link below.
You will find more articles on it here: