My parents have had a terrible marriage for basically as long as I can remember. I have been anticipating their divorce on some level since I was about 11 (I'm now in my late 20s), and I don't know why they don't just pull the plug. In fact, I don't even know why they got married in the first place; they don't enjoy each other's company, they don't have congruent ideas or tastes on basically anything, they're basically incompatible in every way.
I think they both would have been better off if they had split up early, never gotten married and never had children together. They should have married different people, or just not gotten married at all.
The obvious implication of this, of course, is that I shouldn't have been born. This does cause me some existential discomfort. Thoughts occur to me like, "Why do I care so much about the future? Why do I pay so much attention to politics? What's the point of advocating for socialism or trying to work towards a better future? I don't have kids, I can't have kids*, I don't think I should have kids, and I don't even think my parents should have had me. In a better timeline, I wouldn't even be here anyway."
*(I had a vasectomy a few years ago)
I would like to feel a bit more assured about all of this. What do you think?
I can relate to those thoughts and I've just been diagnosed with heavy depression. If you're also tired all of the time you might want to go to the doctor's.
Anyway regarding your parents: Who they are now might not have been who they were when they decided to have you (I know mine weren't).
Either way, you're not responsible for your parents happiness, but I'm pretty sure they're very happy that you exist, they just don't like each other.
It sounds like you're taking on a responsibility that isn't really supposed to be yours, so I just want to say: You didn't keep them together, their unwillingness to accept that they should be apart did. They might have used you as an excuse for this unwillingness, but that's on them, not you. You are not responsible for that, just like you're not responsible for their relationship. They are adult sapient beings who should be able to look at their relationship and realise that they are bad for each other. The fact that they have a child together shouldn't be a complication, in fact it should have made it easier for them to make the responsible decision, so they could provide you with two stable loving homes, instead of one unstable home.
You are not responsible for your parents. They are responsible for themselves and in fact they are responsible for you, because they are your parents. It should not be you lamenting your existence, but them lamenting the fact that they have pushed you to think such a thing. You are not responsible for your parents.