Much of this also applies to relationships in general, outside of Thailand.
In Thailand, there are generally two sorts of lady: Prostitutes, and Mainstream (non-prostitutes). Based on statistics from various sorts, only about 2% of Thai ladies are prostitutes. However, these prostitutes tend to concentrate themselves where the business is, which includes a few square kilometers in the tourist and expat concentration areas in lower Sukhumvit and in Pattaya, and they tend to stand out since they try to get the attention of foreign guys. It is very important to understand that what you see in those zones is very different from what you come across in the rest of Thailand (except other hot spots).
There is a big difference between mainstream Thai ladies and those you can meet in bars and nightclubs. What is often said about "Thai ladies" in general, actually applies only to [ex-]prostitutes, who seem to make up the majority of girlfriends and wives of foreigners, so don't believe everything you read and hear ... e.g., "Thai girls are unfaithful", or "Thai girls just want your money". Substitute the word "prostitute" for "girl" in those sentences and it makes more sense. If you're old enough to read this, and sophisticated enough to use Internet well, then you should be old enough to not believe everything you hear and read about Thai ladies and smart enough to think by yourself...