I don't know how to tell my ex that I don't want to get back together

My ex recently got back in touch with me and wants to start over. I still kind of have feelings for this person, but I can't see us being happy together because they're monogamous and I'm polyamorous, and they aren't open to the idea of being in an open relationship. I've tried to be mono for them before and while they were happy, it made me miserable, and I don't want to go through that again. I don't know how to tell my ex it won't work between us. What should I do?

"No" is a complete sentence. Consensus is not required here. You don't need to get them to agree, or see things your way. You don't need to convince your ex that getting back together is a bad idea. You can just decline to get back together. You know that dating them made you miserable, and you don't want to do it again. Some lines you can use:

  • "I don't want to get back together with you."
  • "The reason we broke up still exists for me, and I haven't changed my mind."
  • "I know that you want to try dating again, but I don't feel that way."
  • "I'm not going to try and argue or get you to see things my way - you just need to know that my answer is no." 
  • "Please don't ask me again. If you keep trying to push for another relationship with me, I'll have to take a step back from even a friendship."

If they won't take no for an answer, do what you need to maintain your boundaries. Block them through whatever channel they used to get back in touch. Take emotional and physical distance. You have no obligation to "tell them" in exactly the right way. You don't need their permission to not date them. Stop worrying about how to tell them - just tell them, and then walk away.