Having had to sack a couple of Thai (male) workers before; the whole "mia noi" thing seems to be a total cultural dysfunction Thai-style: Fights happening at work; mia nois / wives jamming up the phone lines with abusive and threatening calls; the guys sleeping rough after being turfed out of the house; not turning up to work, etc etc.
Seems to be a full-time occupation in itself; keeping the wives apart just for a misguided boost to a fragile childlike ego.