Note: this comment started as a reply to someone else, but it got long enough that it seemed better to post as a top level comment instead.

The throwing a chair thing is scary. It’s easy to excuse this kind of thing early in a relationship, because “emotional blackmail” sounds like a huge deal and it’s easy to argue that “she’s not intending to manipulate me, she’s being realistic about her own mental health”, but emotional blackmail doesn’t require intention.

OP, if you’re worried about her mental health around a potential breakup, then please consider how that same concern would apply for an actual relationship. When she says “at least I didn’t bash my head into the wall”, this sounds like it’s her being honest with you about how her mental health is rocky enough that throwing a chair is a victory. That sounds like it must’ve been scary, even if you weren’t scared for your physical wellbeing, and that can really take a toll on you long term, even if things don’t escalate beyond this.

Consider a scenario where she is bashing her head into the wall, due to an emotional trigger that’s completely separate to you (so you have no personal sense of duty beyond “this is someone I care about who is harming themselves due to ill mental health”. Actually sit and ask yourself how you’d respond to that scenario, because it’s the kind of situation where there is often no winning option on how to react. Physically restraining someone to prevent them from hurting themselves can be dangerous to both people, even when the restrainer has training on how to minimise harms, it also can cause an escalation of the emotional distress even if it is possible to do safely, and it’s ethically dicey in a manner where even discussing things in advance doesn’t make it easy.

I say this from the perspective of someone who has been on both sides of things. There have been times when I was too unwell to safely have a partner. It put us both through a lot, and though I was lucky I was able to repair our friendship after we broke up, it messed me up to reflect on how much I put my partner through. A counter example of a healthier version of this problem is that when I am especially anxious, I may dig my nails into my skin while trying to solve a difficult problem, often without noticing it. I discussed this with my close friend/housemate because they weren’t sure whether they should try to encourage me to stop doing it when we were discussing something difficult, but I said that although this was technically self harm and not ideal, that this felt to me like something it’s better to pick our battles over, because it wasn’t severe and trying to stop it would cause more harm than the harm prevented. However, we both agreed that anything more than that (such as, but not limited to actually breaking the skin with my nails, or hitting myself) was beyond what was safe for either of us. For those more severe scenarios, we agreed that it would be necessary to pause the conversation and leave the situation to give me time to emotionally self regulate. This agreement was only possible because I was in a place where I was able to work towards developing better mental health coping skills (in part due to receiving ongoing professional support and also having other friends I could lean on).

OP, I am including all this detail to emphasise that I am as much concerned for the wellbeing of your partner as I am for you, but seriously, this relationship doesn’t sound viable right now. Hell, even that living situation might not be viable, in terms of how difficult it can be to emotionally extricate oneself from someone you’re living with. If that’s the case, then I realise that moving out all at once would likely not be financially viable, and would feel like an excessively harsh way to end things with someone who you care about. However, if you don’t proactively recognise the ways that this dynamic is already super unsafe and concerning, it just makes it more likely that things will continue getting worse until one or both of you breaks and you have to do it the abrupt way.

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It is a difficult to handle situation, but it may be possible to handle it gracefully. A few pieces of advice (having been on both sides of this):

• “Break up” can feel overly final and it can feel impossible to do in a way that won’t be emotionally explosive. Thinking of things as a “relationship de-escalation” can be useful — not just for minimising hurt feelings for the other person, but also for giving yourself the much needed emotional space to evaluate what your capacity is in this relationship. I cannot emphasise enough though that you should not expect yourself to be the sole mental health support provider for a loved one. It’s not tenable, and will just lead to more hurt. If you’re certain you want to end the relationship, then a compassionate lie may be to frame the de-escalation as a potentially temporary thing, as you evaluate your own readiness for a relationship. It can be tricky to do this well though, because you don’t want to come across like you’re bullshitting and this is just a breakup in disguise. It can be useful to ground this in actual truths, like "if we’d started dating and then moved in together after a while, it would have probably been more gradual. However, because we started as housemates and then this relationship took us both by surprise, I’ve been struggling to balance the intensity of “new relationship” feelings with what that means for people who are living together.

I do actually know a married couple whose relationship started in this way. They deescalated their relationship for a few months and continued living together as friends, because neither could afford new living arrangements. After things had cooled off, they re-evaluated and concluded they did want to pursue a relationship properly, but that it would be best if they were living separately (lest they doom the romantic relationship before it began, as they almost did previously, and worse, risk jeopardising their friendship). They dated, and after a while, moved in together and found it went way better when they had the space to gradually get there. My point here is that “deescalation” isn’t a dressed up term for breaking up, but a legitimately useful thing to do regardless of where you see this relationship going in the future

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• It’s very important that the breakup or deescalation conversation does not focus on the cleaning stuff. This isn’t about the cleaning stuff. That may have been what catalysed this particular stress point, but the problem here is something much deeper. You do not want to be in a scenario where the conversation becomes “I promise I’ll do chores more”. That will likely exacerbate existing insecurity problems, and it’s not wise to put people in a position where they end up making promises they can’t keep (or where you may be tempted to agree to their pleas.

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• Similar but even trickier is that ideally, you want to avoid the conversation coming across like “I am not able to cope with being in a relationship with you because you’re too fundamentally broken to love too mentally unwell for me”. This is hard because unwell brains can sometimes make the most tactful discussion feel like a personal attack. However, this is why being proactive is wise — shaping the tone of the conversation is much easier if there hasn’t already been months of bad emotions stewing on both sides due to increasing stress over a non viable relationship (which one or both of you may be reluctant to see). It’s been a few years since I read it, but I think the book “non violent communication” has things that I found helpful for this kind of conversation (you can find it for free on Anna’s Archive). If you end up using approaches from the book, tell her that — the communication skills that books like this teach don’t necessarily sound the most natural, especially if this approach is new to you, and weird language/framings can cause anxiety to ratchet up to maximum if there isn’t context. Again, here it’s useful to pepper in some honesty: something like “I was struggling to effectively communicate my feelings about things like the chores, and after talking it through with a friend, I realised that I had been overly focussed on things like the chores, which made it seem like it was a problem with you; I think that maybe I had been focussing on the chores stuff because it seemed like an easier thing to focus on when I didn’t know how to reflect on and communicate how I’m feeling about the deeper issue of all these sudden new feelings I’m having for you.”. That’s just an example — don’t say things that aren’t authentic to how you’re actually feeling. Even if you don’t use a book like that, try writing out your feelings in a sort of journal entry (something that’s just for you to work through things) — sort of like you did for this post, but more centred on how you’re feeling about things, especially after reading people’s replies.

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Finally, don’t feel like you need to reply to this comment substantially, or at all. I know how overwhelming it is to get a big reply like this on an advice post. Even if what a commenter writes isn’t particularly helpful to where you’re at, it’s always heartwarming and humbling to see someone put so much effort into a comment that’s intended to try and help. I’m telling you now, don’t worry about it. I’d rather you give yourself space to process everything here. Feel free to reply if you have the brain space though