It's a difficult one. I can totally understand you feeling overwhelmed at the thought of it.
Lots of people refer to the 'sandwich generation' - meaning 'older' mums also having other caring responsiblities.
There comes a point where you have to realistically look at what personal (and financial) resources you have. And also what you can sustain in the long term.
It doesn't help you are this point to judge you for having an eight year old. It is what it is and you have significant stages in a young person's life journey to navigate particularly after the pandemic when so many have missed schooling.
Even after teenage years, they may be independent on the scale of it but still require you being there in the event of an emergency through the uni years at least.
Perhaps as others have said there is a mismatch in your household with caring responsibilites and the mental load/housework involved already in child care and life responsiblilities.
I would start there. If you wish to continue in your marriage - I would look at that. Take one day and one week at a time to try to redress this balance. Consider what it is your are prepared to do going forward. How much disposable income you have to buy in support.
At the same time I think you are right to consider expectations about the future. No wonder you are feeling down about the prospect of taking on all this. How is your own health? Have you kept up with routine health checks - for your age?
I thought the point was valid that caring responsiblities can vary greatly. My own mother after four kids - had been in a role where she was the one who cooked all the time for example. But later in life she entirely stopped doing so - having had enough of it and went back to college and got her own paid work. This brought her and the family a different kind of freedom (and more money).
Time to consider what you are and are not prepared to do going forward and keep revising and checking your boundaries - my inkling is that you will be judged whatever you decide. I often find women are. The teenage years can be rough as you will already know - and also very demanding.
As a single parent I was judged because I prioritised looking after my DD and labelled 'selfish' because I drew my boundaries around caring for elderly relatives as well (there were other siblings in the mix).
It was tough to be labelled like that - but I'm not sorry - you are dealing with the next generation here and it has been tough for them in the pandemic.
Yes, we all are to a certain degree vulnerable when we get older and possilby will have care needs but at the same time we all have a responsiblity to plan for that eventuality and strive to remain as independent as possible surely?
What would be the sense in taking on too much and running the risk of harming your mental and physical health going forward. Doesn't seem that you could sustain the burden of that in any event. You are allowed to have rest and recovery time from caring responsibilities and also heavens about something interesting to do and dare i say it? A bit of joy in your life. Where is that?