Marriages maybe made in heaven but multiple marriages are not. They are definitely planned on earth and most likely due to past life karma. When a person goes through multiple failures in marriage it isn't always the fault of stars. Some fault lies in karma also. But stars do show the way whether a person would see failures in marriage or not. Venus plays a major role in deciding how the married life of a native takes shape. 

     Venus is the planet of love, sex and romance. Strength of Venus along with seventh house generally decides the fate of a native in marriage life. Venus in good condition normally guarantees a happy married life and wonderful marriage partner. Venus in bad condition in dushamsthanas or along with malefics almost always signifies troubles in married life. Normally people who divorce see multiple marriages or multiple failed relationships have Venus in the eight house. Sometimes it is also due to Venus in sixth house or in twelfth house with Sun. But normally it is Venus in the eight house which causes multiple marriages to happen.

Example chart of multiple marriage

• North Style
• South Style

     Concenrned chart is of a native who has has multiple failures in love life. Native has had a failed affair plus a failed marriage behind. Due to placement of Venus in eight house with Mercury the native is a complete flirt and unable to curb his sexual tendencies. Aspect of Mars on Venus adds fuel to the fire and native is prone to flirting openly on the internet. Aspect of Saturn does put some break but native doesn't seem to learn from past break-ups and continues with foolish notions of relationship and marriage. Here also association of Venus in eight house along with Mercury and aspect of Mars and Saturn is the reason for multiple failed relationships and native not learning from them.

     So why Venus in eight house? Well... Venus is a natural benefic. Eight house is the house of divorce, death and dissolution. Law of nature states everything good must come to an end eventually. Eight house is the catalyst for that end to happen. Venus symbolifies relationship. Venus in eight house ensures the native falls in love and than goes through the painful ordeal of break-up or divorce. These process keeps repeating itself until the native becomes disillusioned and seeks an end to love and romance from his/her life. This is first step towards spiritual progress. 

     There are always exception to the rule and not everyone with Venus in eight house sees multiple marriages or multiple failures in relationship. But with Venus in eight house there are plenty of opportunities in life for getting into a relationships and chances of seeing break-ups in those relationship.