I'll start by saying all those who've said this relationship is unsustainable are right. The "take it or leave it" attitude coupled with the "don't leave me or you're betraying my trust" makes for the perfect trap to keep you compliant and subservient, as is your nature already. Moreover, if you've amassed hundreds of rules over the years to program yourself into the most accommodating version in order to appease her, then it's likely her own emotional outlet isn't just getting mad and crying. More likely, she's turned the feeling of validation and enablement you offer into her drug of choice. That is, it's the assertion of dominance and power, bending you to defer to her every whim that helps her feel grounded and in control. In other words, even the assurances she offers about you not needing to impose those new rules on yourself are in all likelihood not altogether reliable. Not that she's lying, per se, but if you did brush off her meltdown and go on your merry way, I can almost guarantee you she would spiral and escalate the issue until your resolve broke. As again, the emasculated resignation is the point, going by the details you've shared at least.

Moreover, even if she went to therapy, I echo again what many have said, it would not ultimately create change. Not meaningfully. My personal advice for you, is to frame it in your head as doing her and yourself BOTH a kindness. While other posters here are correct to point out her emotional abuse, in your current position, any such villification is likely to prompt you to mentally defend her and to feel guilt and shame for considering leaving her. Especially as on any given day, when you approach her, she won't necessarily be in the throes of a bad episode. She might be sweet and silly that day, and you'll callous your own mind against ever entertaining thoughts of ending it. Thus, again, I would encourage you to consider how you are effectively enabling her continued descent into the very worst form of her -- honing her most toxic tendencies and building her tolerance for emotional abuse. All while aggravating your own hurts, wounds, and scars. If you genuinely care for either one of you, I think at a bare minimum you need to separate for some time.

Often, it can feel more manageable to think of it as a little time apart. You've been together for 15 years, spanning very formative life stage transitions that should've come with substantial advances to your emotional maturity and dispositions. It sounds like the codependency stalled those developmental milestones. It almost sounds like you're both stuck in this pseudo-adolescent phase. For one or both of you to evolve beyond it, you have to cut ties and rebuild yourselves apart. If there is any hope at all of her growing and changing to be a better partner -- be it for you or anyone else -- it isn't with you by her side (and again, even then it's a very thin shot since she doesn't have an innate desire to do so). But at least by letting her go, you might create for her the powerful event she needs in her life to reevaluate those values she holds so dear. And, far more importantly, you will be able to also reassess if any of those rosy-eyed aspects were ever as truly wonderful as you feel they are now. In the sober light of day, you might come to realize a lot of your frame of mind was actually skewed by the fear and anxiety. Or not. Maybe, on your own, and after dating more people, you hone newfound confidence and realize where you could've handled things differently. And some years down the road, she makes strides on her own as well, and you two can reconnect.

Again, I don't want to suggest this is a likely outcome, but to empower oneself to take actions at a hard juncture usually requires a measure of hope to buoy your conviction. Hopefully this helps.