I suspect this article is not completely unbiased, but it may help you build up a better understanding of the "Mia noi" phenomenon.
The Mia Noi or Minor Wife in Thai Culture: Having a Mistress in Thailand is Actually Quite Common
Many Thai Men Have Mia Nois or Minor Wives - It's All Just Part of Thai Culture
Many men in Thailand, both rich and poor, have a 'mia noi'. A 'mia noi', roughly translated, means 'minor wife' or mistress and has been common in Thai culture for centuries. Even in modern day Thailand, many Thai men will have a mia yai, a major wife (the main wife) and then a mia noi. The mia yai takes care of the family and the kids; the mia noi takes care of the husband, although sometimes she might have kids with him too. This practice is still so prevalent in Thailand that, only a couple of years ago, a female senator gave a speech asking male senators to not have a minor wife. Of course, I'm sure most of them weren't listening.
The Mia Noi in Thai History - Having a mia noi or minor wife has been going on in Thailand for hundreds of years. Polygamy has always been an accepted part of Thai society with those men who were wealthy having more than one wife, some of them having several. In fact, the wealthier you were, the more wives you had. In modern life, this really hasn't changed much. Of course, it's not talked about and you're very unlikely to find a man who will admit he has a minor wife. I have, however, met two Thai women who were minor wives and one had a child with her 'husband'. In one of these cases, the major wife didn't know about the minor wife. In the other case she did. But, if the minor wife is common in Thailand, what do major wives think about it?
The Major Wife and Her Thoughts on Minor Wives - Surprisingly, when the main wife finds out about the minor wife, it's not usually like it would be in the west. No demanding the husband breaks up with the minor wife, no threats of divorce. Instead, often the major wife will look at it like, as long as she and the children are being taken care of, she's not going to make too many problems about the minor wife. Overall, most Thai men still tend to stay with the first wife so, having a mia noi, some women think, can make the first marriage more likely to work out. If they push though and insist their husband break up with the minor wife, they also know there's a chance he will leave them for the second woman. So, it's easier just to stay quiet.
Major Wives in Modern Society Have Money - One thing that is changing in modern Thai culture though, especially in Bangkok, is that a lot of major wives now have jobs and money of their own. In the past, it used to be that the money for the family belonged to the husband so, in this case, the major wife wasn't likely to rock the boat when it came to mia nois as, if the husband left, she might be left in financial straits. Now, with major wives having their own jobs, some of them don't care if the husband leaves because, unlike in the past, they can take care of themselves and their kids without the need for money from the husband.
Thai Men and Minor Wives - Overall, I can understand why many Thai men have a mia noi. In Thai culture, Thai men are not usually open with their wives about many issues. They don't talk about personal problems, they won't tell them about problems at work, and they certainly don't seem to talk to each other about relationship problems. This often seems to change though when they meet a girl and she becomes their minor wife. For some reason, Thai men are a lot more open with their minor wives, telling them things they would never tell the major wife. It's often a release for them, just being able to talk to someone about problems they could never talk to their wife about. Smarter more modern Thai women, though, are realizing that being more open with their husbands makes it less likely the husband will take a minor wife and can also create a happier married life.
As a Westerner living in Thailand, I don't necessarily think the minor wife system is bad. The husband is happy because he's not so bored with just one woman and he also has a person he can actually talk to. And, as modern women in Thailand often make their own money, the cost of having a mia noi can be a lot less than it used to be. The major wife is sometimes also happy as she has less pressure placed upon her for sex, she knows that her husband having a second wife makes it less likely they will get divorced and, as long as she and the kids are taken care of financially, this set up often works fine for her.
As for the mia noi, the couple of minor wives I've met were very happy with the situation. As independent women, neither of them wanted to be with a man 24 hours a day, seven days a week. Being a minor wife allowed them the advantages of having a man in their life but with not many of the disadvantages (no dirty laundry laying around, no guy plonked in front of the TV every night, no one constantly telling them what to do).
In fact, you could call the minor wife a win-win situation for everyone involved.
Link here:
http://www.associatedcontent.com ... culture.html?cat=16