As we were mostly, if not all, bachelors the majority had local girlfriends, many got married. It is either one of the pitfalls or pleasures of sending single men to exotic corners of the world.
Also it was very difficult to live in Vietnam if one did not have a maid to take care of one's day to day needs. Then one needed someone to take care of the maid etc. I always believed Vietnam to be one country in a state of civil war. This was in contradiction to the official US view. They had always been one people throughout history and eventually would be so again.
There was a distinct difference in character though between the North and the South. In the South they were much more easy going, in fact had an easier life, the war apart. They were very quick to anger and the fury of their women was something to be avoided. This anger though would last an hour or a day, no grudge would be held, and everything would then return to a state of loving normality. Generally they were absolutely faithful.
The North Vietnamese had a much harder life and had never accepted French domination. They were generally very slow to anger. It was said that they would wait ten or twenty years if necessary before exacting their revenge. Easier to get on with, more practical, but one was never certain of what they actually thought.