spite dating
Dating someone new just to get back at an ex or make an ex jealous - usually leads to a spite marriage. Similar to a rebound but you act like more than a hookup and post obnoxious pictures on social media about how happy you are now and actually convince the new person it's a real relationship and not spite dating.
"Do you think Emily realizes that Luke is just spite dating her to make his ex, Nikki, jealous?
spite date
a date accepted because one is angry at a third party (likely a former girlfriend or boyfriend) to prove you can do better
Jane went on a spite date to prove to John that she can do much better.