Get everything set up to leave. A new place to stay, a way to move all your stuff quickly, maybe a new phone number.

Then just do it. Tell them and rip the bandaid off! Maybe have no contact for a while (or forever).
If you have to leave then leave. It hurts but things will get better after a while.

You have nothing to lose at this point. Keep that in mind. Find the kindest way of being honest. This is not about them, it is about how you feel and what you need. So please be compassionate because they may be very hurt. That being said, you also have feelings and you are here to live your life, not another's.

The gist of it:
You are not feeling good in the relationship anymore. You tried to make it work when they asked and it hasn't worked for you. You love them enough to be concerned for their feelings and am not making this decision to hurt them. You are making this decision because you are not happy and no longer want to try with this person any more. You appreciate all that you have been through and none of that will be erased. You have grown and changed and so have they. Sometimes people grow alongside each other, and sometimes they grow in different directions. This is what you are experiencing. If you want to be friends, offer that, and only if you are capable of following through. Otherwise, staying together because it's easier or because it's financially better is not enough.
Let them know that you can see and feel their pain. Also acknowledge there will never be an easy way, and that you have already decided. Let them have their emotional expression. let them be angry, sad, whatever. Let them ask why, and hold firm on your decision while allowing them their moment. The kindest thing you can do is allow their moment and their closure.

That is what you say and do. And above all, be compassionate while being honest. Compassionate. So, for example, if all you love and feel compassion for is your dog, and it pains you to make your dog sad but it's so much easier to blow off people, and if that is the only thing that stirs compassion inside you is how you'd feel if you accidentally hurt your dog, then refer to that feeling you have as your benchmark. That feeling of regret and sharing sorrow, that is compassion.

I don't want anyone that doesn't want me. Not into holding anyone prisoner, or taking measures (like having kids) to manipulate them into staying either. Why the hell would I put up with feelings of resentments, regrets from either side, and of feeling perpetually disliked, and unwelcome in my own home? One of us would be leaving, that's for sure.

I understand. I ended a long term marriage, but only after many years of being unhappy. It was very difficult for both of us, but eventually I just had to be true to myself, because I felt like I was dying day by day in a relationship in which I felt completely alone. If you feel like that, you have to leave. Yes it will hurt them, but you may be doing them a favour in spite of that. My ex found a person much more compatible for them and has been happily married for many years now.

... two marriage-like relationships end after about 3 years. That was enough for me, I can't do it again, because if it works out, great, but if it doesn't, those two things nearly wiped me out---is this because I have a soft skull? Maybe, but the "soft skull" doctrine is that if you tap someone on the head and crack his skull, you don't get to say 'well, that wouldn't have cracked a normal person's skull!' you're liable for cracking the skull.

IMO the pathetic thing is your talking about this as though you care at all about 'the pain you'll inflict'---you don't care about that, all you care about is that this individual will, apparently, try to convince you not to cause him (or her) pain. Depending on age, if you're female and he's male, this is pretty much a death sentence. This whole "oh, he'll just have to put himself out there" is advice for women by women that men have picked up for some reason. A woman, almost any woman, can just put herself out there and some many (not every man, but some) will bite. For some men, given a combination of age, financial position, bad bone structure, etc. no women will bite.

If you want to leave and you don't need signatures on anything, rather than doing this ridiculous game you've already done before, just write a short note "I am leaving you. Please do not contact me in future. Yours truly, Timewaster." You don't have to do anything else, and you don't have to have any further contact if you don't want to.

... both women who left me psyched themselves up for it (I am a sucker for punishment, I remained friends, had talks about it afterward!) by talking negatively about me with their mothers and girlfriends and employers. I dunno if you're a woman, and I say that because men tend to be less able to shit-talk women than vice versa, but if you are a woman, you shouldn't have trouble finding other women to egg you on. My girlfriends didn't!

Gentle Confessor, you don't need your partner's permission to leave. If that's what's best for you, you need to do it, regardless of what your partner (soon to be ex-partner) says. If you live together, just set a date, find alternate accommodation, get some friends or family to help you pack up and then... just.... leave. I can guarantee you that your partner will try to talk you out of it again. Inform him/her/them that it's not up for discussion or negotiation. It's not up to you to manage your partner's feelings nor is it your responsibility to do so. Sure, leaving a long term relationship is difficult for both parties but, it that's what you need, then you need to stand up for yourself and do it. Don't be manipulated or coerced into backing away from your decision, even if it means physically removing yourself from your partner's company for a few days while s/he/they process your decision. (NOTE: If your partner is violent, then this is a different scenario entirely and you should ignore my advice, but you don't mention anything like that except for the obvious fact that your partner doesn't respect your boundaries.) My sense is that s/he/they has reasons for not "letting" you leave and none of them are for your benefit but theirs. Once you extricate yourself from this relationship and establish your own space, I would also highly recommend that you speak to an accredited counselor about how to establish healthy boundaries so that you aren't persuaded to fall back into old, familiar patterns. Best of luck to you!

Ya just step out the back, Jack...

"It's not up to you to manage your partner's feelings nor is it your responsibility to do so"

... that's why we're allowed to tell racist jokes in class at UBC, nobody is responsible for anyone else's feelings in 2019.

Stop teasing people when you know u dont mean it.
The back , waiting just like that. Huh
Prove it.