Bro, in Thai. Anything is possible.
There is no need to legally marry a thai ger if you are already married in Singapore. In thai, as long as you hold a custom marriage in the village, you are consider married even though you do not have the paper. Most of the thai gers I know of are OK with this kind of arrangement,
If you ask me y. I tell you the reason. NO STRINGS ATTACHED. If one day they get sick of you and wants to OFFICALLY MARRIED TO ANOTHER GUY, they are allow to do so without any issues.
Of course, I have seen cases whereby the thai gers already know that the guy have a wife or gf in singapore but still have babies with him. My advice, IF YOU HAVE THE $$ and can support 2 FAMILIES, GO AHEAD.