What's the right way to break up with someone you have been seeing for 1.5 years these days?

I was in a six-year relationship, and when I got out of it I was the definition of emotionally unavailable. I have maintained communication about that throughout, but I now find myself having been seeing someone 2-3 days a week for the past 1.5 years. We have been poly that whole time, and I have dated others, but none for very long (Mostly less than two months, although one or two hung around longer and/or had unicorn experiences with me and this woman.) All of those I politely broke up with over text, talking about how wonderful they were and how I was breaking up with them for reasons unrelated to them. My perception is that is the way to handle those situations.

This on the other hand... honestly I have only broken up with someone else long-term-ish once before and it was the hardest thing I have ever done. This situation is rough for the same reason. She is nice, kind, a nympho, and has other pleasant qualities. But I can't see myself respecting her enough for long-term, nor do I feel like she could carry her weight as a partner, which I think means I need to figure out the best right way to set both of us free. She has continuously respected the space I want, but has also made clear her interest in long-term relationship and she keeps gently pressing on moving toward being treated like my girlfriend/primary. That is leading me to this breaking point, unfortunately.

Ending A Relationship Necessarily Engineers Serious Tension

Ghosting is obviously the wrong way to do it, EARNEST, whether you're talking about six years or six months. Or six weeks or six days. (Six hours? Debatable. But why not err on the side of not being an asshole?) And if your gut is telling you a text would be inadequate then... yeah, texting this woman something like, "Hey, thanks for respecting my space and all those awesome threesomes, you nympho, but I'm out," is not onluy inadequate, it's cruel. She invested a year and half in you and was the right semi-regular/semi-partner for you over the last eighteen months, EARNEST, and you owe her the courtesy of a face-to-face breakup.

Which means you'll have to ova up and say something like this to her in person: "You're great and I've enjoyed getting to know you the last year and a half. But you want a long-term commitment and you're not a person I can see myself with over the long-term. I'm sorry but this is the end for us." While that's never a fun to say, EARNEST, it's a lot less fun to hear. But there's no way to spin or avoid the pain you're going to cause her. But if you're a grownup you'll breakup with her like one.

With that said, EARNEST, I'm concerned you describe this woman as a nympho without making it clear you consider that a compliment. Doubly concerning, your next sentence opens with this: "I can't see myself respecting her enough for long-term..." Considering your own sexual interests and practices—your interest in threesomes and open relationships—you should want to be with a woman who's just as interested in sex and just as interested in "unicorn situations" as you are. So I hope you're not one of those "sexually adventurous" straight male hypocrites who can't see themselves with a woman—who can't respect a woman—who enjoys sex just as much as he does. If it's her political opinions or her belief in astrology or her climate change denialism that cost her your respect, EARNEST, that's understandable. But if you don't respect her because she enjoys sex... and you enjoyed having sex with her... and that cost her your respect... well, that's some shitty ass Madonna/whore complex misogynistic bullshit right there.