@Anfi *******
if you have a thai parent (whether you're born in thailand or not you're ALREADY a thai ;) )
To qualify for citizenship based on marriage to a thai a male foreigner has to be married 5 years, be legally working work permit, file thai taxes for xx number of years and a whole bunch more of paperwork.
Foreign women marrying thai men have a far simpler route to go.
Google is your friend. There are a TON of topics about it.