if there's no net gain, don't damage yourself for someone who's already damaged.
if you genuinely love this person and want the best for them on every level, then act accordingly. but keep in mind that you also need to want the best for yourself, too. it's up to you which bias you choose. you also have to evaluate whether or not they feel the same way.
if they kill themselves while you're with them anyway, are you going to blame yourself? if they kill themselves as a result of you leaving them, are you going to blame yourself? lastly, would they directly blame you, ever? the answer to all that stuff is gonna affect a lot, too
beyond this, your moral standards and how you truly feel, how you cope with things that hit said feelings and standards, and what people you've got around are going to ultimately determine whether or not this all improves - for better or for worse.
what I mean by this is: it's not just in your hands, it's in theirs, too, and if you two are in a relationship, that has to be understood regardless of mental illness, regardless of who dies, regardless of how much stuff either side is dealing with, regardless of who's causing whose pain or how much or helping how much of it - it all has to be resolved in stride, and you can't pin too much on yourself or too much on them. otherwise you cause damage and leave unhealed wounds and stuff because you never fully went through the full situation.
in short: if there's stuff, and you put it aside, it has object permanence. you didn't get rid of it. you just let it affect you/them/both of you more. differently, but more.
pinning stuff on either person can help you cope, but it won't help the situation because it's still there, instead of resolving it which would actually provide closure, solutions, and lots & lots & lots of handy dandy lessons for future reference. it's gonna take real work to get through something like this, especially since your partner is as damaged as they are. and honestly, it's up to you, not the blockland forums- nor I.
just saying, if you work through that stuff, if you're able to work through that stuff, you will clear past it. you will manage. you will grow closer as people and grow stronger, and you'll grow more mature and eventually more happy.
but it's really up to you, and it's up to them. like I said, if it seems fruitful and you're willing to do it, do it. do it carefully. do it with loving love. but if you can't, or if it would have no net gain, then... don't. do something better, or something else, or something you can do, I guess.
just go with what you think is best, and be confident in that. the only reason you can ever blame yourself is if you were given a clear list of options and you consciously chose a worse one. (or if you didn't decide to be careful)
I date a dude (but sometimes not a dude) who has experienced physical and loveual abuse and suffers anxiety to the point of panic attacks that cause him to pass out; major forgetful episodes; rare occasions of psychosis; incredibly surreal and vivid hallucinations; depression to the point of losing the ability to walk or move, extreme pain in his joints, slicing his skin to ribbons without knowledge of it, tearing his arm open with a cleaver and at one instance, fellating a shotgun barrel that was pointed at him by his brother to name a couple Self Delete attempts; brutal traumatic flashbacks that yank him out of reality; dysmorphia and dysphoria capable of inducing intense depressive episodes. after 7.5 months he's retained spectacular functionality and he's coping amazingly
I mean stuff's bad, but he doesn't wanna die anymore and he's far far far more healthy and happy, and his future looks bright now
but yeah, we manage because we're open and honest to eachother and are willing to genuinely do our best for one another and ourselves, despite all the bullstuff. if you're willing to offer the same, and she is too, it should do wonders. (you still have to be prepared for if it doesn't)