As someone who has cPTSD with associated panic attacks, depression, anxiety etc., I have complete sympathy with your struggles with mental health.
However, your daughter, just like my now adult children, are not responsible for your mental well being.
You need to separate the two issues out. As I have read this, by pinning what you see as awful changes to your daughter into the boyfriend, it means you are making him out to be the focus for all of your issues. ‘
‘DD always out with boyfriend -> she’s rarely here with me -> the bathroom isn’t tidy -> I’m crying myself to sleep with having panic attacks -> therefore the boyfriend must be the issue!’.
However, from an external perspective we can see that you have an independent 18 year old daughter, who is not only doing A Levels with the aim of going to University but is also holding down a part time job, has a boyfriend, keeps a relationship together with her Dad and her Auntie on a seemingly regular basis, has several younger siblings from both Mum & Dad she loves and also feels secure & comfortable enough to be a pretty normal 18 year who wanders back to Mum for laundry/advice/a good feed and a change of clothes.
Saying that your 3 year old is upset when 18 year old DD doesn’t come around sounds a little ‘laying it on thick with a trowel’ (as my Mum would say, oh the irony) in order to provoke sympathy. My then 3 year old DD was upset one day because she’d dreamed she had a pair of fluffy pink slippers, only to find out that her real fluffy slippers were purple when she woke up, but because she was 3 then, by having a hug & reassuring her, then redirecting her with an activity to stop her from focussing on her imagined apocalyptic level slipper trauma.
And I mean she was almost inconsolable that morning. You’d think King Herod had slaughtered her firstborn by the wailing that ensued. By not focussing on the bloody slippers, and continually reminding her about the blooming pink dream slippers, she was absolutely fine.
Are you sure, in your scenario, that your 3 year old isn’t being reminded by you that her older DD had promised to be there at a particular day or time? Like, “Aww DD, older DD hasn’t come to see you again, oh isn’t it awful!” Or if she asks about older DD you’re not saying to her, “Oh little DD! She hasn’t come around again! How awful she is!”? Because if you are, then all you’re doing is reminding her about the damn dream pink slippers.
What you should be doing is saying, “Oh! Don’t worry! We’ll see older DD another day! Now, let’s go & make mud pies or build an atom bomb!”. You know older DD is mostly in & out, so why perpetually remind your 3 year old that older DD isn’t there, and how unfair it all is?
And as much as you believe your mental health issues are being hidden from your kids, please realise that they aren’t. Kids, even 3 year olds, are very astute and are sponges when it comes to their emotional environment. If you are always angry or upset when older DD is in the house, then your 3 year old will try to placate or make Mummy better by echoing the same sadness back to you, as she’ll see that as a way of empathising with you as a kind of child like solidarity.
Likewise, if you are upset about DD, little DD will be upset about older DD. If you are angry with older DD, younger DD may hyperfocus on older DDs absence as she will see that as being the right emotional thing to do, as heck, that’s what Mummy does, and Mummy is always right, eh?
Continually reminding younger DD that older DD isn’t there or is the reason for younger DD being sad is incredibly unhealthy for everyone.
Going to the GP to get further treatment for your anxiety, panic attacks etc., is a very good first step. Hyper fixation on pinning every issue on either the boyfriend or older DD is neither helpful or healthy. As I said at the beginning, your children are not responsible for your mental health. You cannot demand they do X, Y or Z because you’d find it easier to cope with (and what DD is doing is pretty normal for a teenager if I’m honest). What you need to be doing is finding better strategies for dealing with your own mental health, because that will be having a detrimental affect on not only the 18 year old (could it be of Mum’s always on her back or being blamed for everything she doesn’t feel welcome at home?) but on your 3 year old as well.
You remember I said about the fact I have cPTSD? A healthy chunk of that was due to the mental health issues of both my parents (as well as being SA’d as a child, and adult, plus DV throughout my childhood). They were violent to each other and me. If I wrote everything that happened to me as a kid (and even as an adult by my parents) then I’d be pissing over everyone’s Monday morning. Even when they thought they were being normal, they weren’t.
So as to break that awful cycle I worked hard to accept & find solutions so that I wasn’t going to be the mother whose emotions we all had to tightrope walk around. And the same with my Dad. Everything was always someone else’s fault, and they never took responsibility for anything that happened, ever. Home wasn’t a welcoming place. It wasn’t open arms & comforting hugs when you needed it. If you had a problem, it was always, “Yes, but my problems are so much worse!”. I didn’t spend a lot of time at home as an 18 year old either, and as such became the font of all blame. Mum still maintains that my having a child at 19 (without their help) was the reason my Dad left (and I’m now in my fifties!). So he must’ve fallen and accidentally slipped into the vagina of a younger woman then (multiple times, clumsy Dad)?! I could’ve tidied every inch of the house and I still would’ve done it wrong (and often did, Mum was always in front of the TV with her hand on her forehead in the ‘oh, it’s all so awful and it’s all your fault!’ pose, from my earliest memories until a couple of months ago when I last saw her).
Whereas in reality, I wasn’t at home because it didn’t feel welcome, I worked every hour I could to help set me up for Uni & achieving escape velocity from my parents.
With the greatest of respect, this is not DD’s problem to solve. Please, try & take the advice the majority are giving you. Kids aren’t there to mend us, it’s our job as parents to support them. Teenagers are unconsciously selfish at times because, they’re teenagers (have taught & volunteered with thousands of kids from 5-18). I wish you well.