This is one mistake alot of people make that is causing a lot of problems into their relationships/marriage bringing in the pain, the anger, the frustration and others from a previous relationship into a new relationship.
Everything that happened in the past has happened so let the past be in the past, stop bringing the past into your future you will end up hurting yourself and people around you, so bury your past and give your future a chance.
For example as a Lady your ex boyfriend cheated on you, that was the reason you broke up with him, you then conclude that all men are the same and that they are all cheaters, luckily you get married or into a relationship with a Man who is very faithful but because of your previous relationship you start developing insecurity issues, you keep suspecting that he is cheating on you, you keep doubting the relationship until you make it crash.
You’re a guy the girl you dated left you because of money then you assume all girls a gold diggers. So when you start dating a girl who loves you genuinely you think she’s a gold digger you treat her anyhow and then before you know you have lost her.
Avoid taking the drama from your past relationship to the new one, let be past be in the past, forget about everything that happened and give yourself a chance to happiness.
Remember the person that hurt you has gone his/her way, now you’re with a new person, an innocent person who do not know what happened in your past relationship, if you want to have a revenge please go and meet the person that hurt you and leave your innocents spouse alone.