I'm upset with my ex-boyfriend.
Why are you upset with your ex-boyfriend?
He was very kind and loving and when he broke up with me it broke my heart.
It sounds like you went through a very difficult breakup with your ex-boyfriend. It's okay to feel hurt by this breakup, but you have to move on with your life at some point. Make sure that you talk with someone if you need help getting past this.
It would be fun to make his life miserable. Can you imagine how boring life would be without hate?
Even though you are upset, it is best to move on. Holding a grudge won't do anything good for either of you.