I'm going to leave my partner for someone else
Why are you going to do that?
My parents want someone else to be my partner.
If you are not happy with your partner then you should break up with them before starting a new relationship. It is hurtful for your current partner to know that he or she is so easily replaced. You should also think about if you really want your parents to have a say in your romantic life as what they want may not align with what you want.
I am doing it because it is what my parents want. They could be right, who am I to disagree?
While doing something because it is what your parents want not what you want could end of bad, it is up to you. You should however make sure that you end things with your spouse before you start something with someone else.