Being married to two people at the same time is called bigamy. It is illegal and you could have him charged with a crime. Either way, he loses. If you ARE found to be legally married, you are entitled to make a claim for alimony, equitable distribution etc during the divorce proceedings. Plus child support of course.
If you are found to NOT be married due to his being married to someone else at the time of your marriage, then he can be charged with bigamy AND you have a very good chance of winning a civil suit against him for fraud and misrepresentation.