Janet Jackson has been married three times. Her first marriage was in 1984, to singer James deBarge when she was 18. This marriage was short lived and there were no children - there were rumours of a child but this turned out not to be true.
Her second marriage was to Rene Elizondo Jr, an actor who she started dating in the 1980s and married secretly in 1991. The couple managed to keep their marriage secret until they separated in 1999 (they divorced in 2002). Again, there were no children. The couple gave their reason for keeping the marriage private as thinking that their relationship would have a better chance without the media publicity. It did last about 14 years in total, which is a long time for a celebrity relationship.
It has now been reported that she has married a Qatari businessman, Wissan al Mana. It seems that they actually married last year, but once again preferred to keep it secret.