> it's almost like I've been using only 10% of my mental capacity for work (the rest was on dating/dealing with breakups/dealing with depression/gaming/...)
I think that could give an indication of what might be wrong here, I can relate (somewhat!). I work for a top-flight tech firm, straight out of school, for about 5 years or so, and for a long time I felt just like that: I focused for a very long time on achieving the next goal - passing an exam, getting into University, getting that job, and not really focusing on what that was all for, not really focusing on my personal life etc. Once I got my job I was like “what is all of this for?”
So I changed tack, I rotated positions at my job, I tried to “live with purpose”, do something with a super-high impact, and not put myself under such relentless pressure to succeed. It may not feel like you have a super-high impact, but I’d say you do - the services you run help to improve literally millions of people’s lives. Try to think about it like that, instead of “I’m not living up to my potential”, think about the enormous impact you already have. If you just don’t find the work interesting, talk to your manager about the possibility of a secondment to another team.
I’d also advise that relationships are hard, and it is OK to feel miserable when they end. But one thing I only realised recently is that if your misery extends by more than a two months, it could be indicative that you need to see a doctor. Depression is a terrible condition that’s still (IMO unfairly) stigmatised and it’s often hard to disentangle from the rest of what goes on, but it is not a weakness to admit that we all need some help sometimes. If you need an impartial but sympathetic ear, you can find my email in my profile. Good luck! :D