At the time of marriage, you should not have a married spouse who has not divorced his previous spouse. If you are a divorcée you can enter into a marriage again only if your divorce is complete.
Neither party should have a spouse living at the time of the marriage. You can file a civil injunction to try to stop your spouse from getting married to someone else.
If your spouse is still alive, it is a crime to be married to another person. Your first spouse can file a criminal case against you. This is an act of bigamy. This is not an easy process because the first spouse will have to produce concrete proof – even another child being born out of the second marriage is not enough.
If this is proven, you might go to jail for up to 10 years and also have to pay a fine.