There are any numbers of reasons why men leave pregnant women, and I hope that you have never found yourself in this position. This is the kind of situation where prevention is better than cure.
Anyways, why would a man marry a woman and when his wife is pregnant, leave her?
Usually this is very sudden and unexpected, and unfortunately not very common, but even once is one time too many. If it is unexpected with a married man to leave his pregnant wife, then it is much easier to identify the kind of man who would abandon his pregnant girlfriend. This is where it is better to take your time and use your common sense before getting physically involved with your man.
Take your time to really get to know your guy before getting too intimate, as the intensity of passion once aroused tends to cloud your thinking and reasoning. When you have been together for a little while, there will probably already have been some signs that the man you love is a loser.
I have seen and heard women excuse their man's bad behavior. You know the things they say. Some things like, "you do not know him like I do," "he is a kind man deep down," "he has had a hard childhood," or "it is a guy thing," and they use that to cover for the fact that he is being selfish, inconsiderate and disrespectful. If this sounds like your situation, you may benefit from some counseling to help you understand why you are attracted to this kind of man, or would accept a relationship like this.
In truth, there are some men who for whatever reason do not like women, and who secretly enjoy mistreating them. As much as these men do not like women, they are drawn to date and surround themselves with women. They get a kick out of treating their girlfriends like trash and then watching them come crawling back repeatedly. If his girlfriend were wretched enough to get pregnant, it would not be surprising if he left her as soon as he knew she was.
If your man is abusive in any way, emotionally, verbally or physically, then no doubt he will be the kind of man that would leave you when the relationship does not suit him anymore. Take care that if your man displays one or more of these negative qualities that you do not get pregnant, placing yourself and your baby at risk. The abusive behavior is likely to increase if he stays and does not leave you.You would be better off if you left him.
Therefore, if your man does not treat you with a genuine affection or respect, and he shows signs of being abusive in any way, then it will not surprise you if you become pregnant and he decides to leave. There are many reasons why men leave pregnant women and most men could not tell you truthfully what they were, because they may not be fully aware of the full extent of their true feelings themselves. Most "real" men would use the term "man" loosely when it came to describe men who treat their women this way.