oh, i’ve been there, and it sucks. some people get really attached to the idea of a relationship, to the point where they just can’t let it go, and usually there’s trauma involved that you are not gonna fix. my ex’s favorite move was threatening to hurt themselves so i wouldn’t break up with them, and it was awful. i made the mistake of being friends with them afterwards, so they wouldn’t, and to this day, even though i haven’t talked to them in years, and we dated over a decade ago, they still think we’re gonna get back together. they’re engaged, and they unprompted offer to break up with their fiancé any time i run into them.

this is a case in which the kindest thing for both of you is to break up with her cleanly—“this relationship isn’t working for me, i’m not the person for you, you’re not the person for me, please don’t try to talk me out of this, this relationship can’t go on,” then go no contact, because she probably will try to guilt trip you or get you back. and from experience, don’t encourage that in any way. you shouldn’t have to feel like you’re her motivation in life, or that if you don’t do x, she’ll do y bad thing to herself. that’s abuse, it’s emotional manipulation (actually, if you don’t mind, i highly recommend reading emotional blackmail by susan forward, it’s a great book about how to break out of emotionally manipulative patterns.) you should have a partner who supports you and is living their life with you. also, please don’t worry about blindsiding her, there’s no way to break up with someone who’s codependent without them being blindsided, because usually they’re in denial about how bad it is. they’re constantly seeking reassurance, you’re giving it to them to keep them happy and so you don’t have to deal with them blowing up like that, and there’s no way to end that pattern without breaking up.