Lived in Thailand for a couple of years from 2009-2011 for work, then moved to Hong Kong for a couple of years and Europe for a year. Ended up back in Thailand in 2015 and only lasted a year and a half that time. Now my wife (she is Thai) and I are living happily in Argentina as a couple of gringos.
Certain things about Thailand just wore me down after a while. I'd say the biggest nagging issue we had was focused around quality. Some things may be cheap in Thailand, but if you want good quality it will cost the same or even more than it would in Europe or the States. If you want to buy a condo, the quality is sub-par, prices in Bangkok are absurd and there are better deals elsewhere. constantly being seen as an outsider, the token white person, etc. also cut down the honeymoon stage.
If you love the cheap stuff and MSG in your food and constant sweating, then Bangkok is a delightful place. But if you have a good job, want nicer things, want to invest and buy property, and care about your health and general well-being, Thailand is not the right place to settle down. This is just our experience, so take it as what it is. Others may find the complete opposite to be true.