Thanks for your input. As I have more or less poured my heart into this post, such a short reply feels somewhat unsatisfying though. Hence the push.

Let me make the question a little more concrete: Assume
1. You want to HAVE a PhD at some point. Most likely the PhD will improve your quality of life as well.
2. You know that while you're doing your PhD you'll go through immense suffering. You'll spend many years having low self-esteem and feel like you are 'postponing' your life to a later stage.
Would you still do it?

Hi there.
Your post resonates very much with me. In fact, I have written a very similar thread (that is currently pending approval).
I am constantly fighting an inner battle of quitting and 'finally getting started', as the clock is ticking. People who themselves want to push through will give you compelling advice to push through. People who themselves lean on quitting will convince you that's the right choice. Let me argue for quitting, just for the sake of argument:

Finding a job you like is going to be hard either way. The search for a job however is a temporary state. If you know what you want, you will simply keep working towards that. After you got there, most of your lifetime will be spent working your dream job (or something close). How you got there, and the fact that you once quit a PhD will merely be your personal history. The PhD may or may not make the search easier, but if it makes you UNHAPPY over an extended period of time, it's not worth it.
To make it sound scientific: Just maximize the integral of happiness over time. Alternatively, here's an extremely easy flowchart for life decisions: 1. Are you happy right now? Yes: continue. No: change something; goto 1.
Sure, sometimes we have to bite our teeth and defer happiness. It's just a matter of quantification and extrapolation.

I have come up with this plan for myself: "Unhappiness-boxing" (akin to timeboxing). Limit the number of unhappy days you are willing to spend from now on. I have picked 150. Each day I feel unsatisfied I cross out one day, on better days I don't. You may also cross out fractions of a day. The day I reach 0 is the day I will quit no matter what. You can also plot how you use up that unhappiness-tolerance over time. No idea if this works for you, but this concept helps me cope.

Best regards!

The problem, I think, is this: I was unhappy, because I did not measure up to my own standards of success. My ultimate goal is still to get into a high-qualified job in the industry, in which my creativity can thrive. With my current qualification, that does not seem to be possible. Thus, getting a PhD is a means to an end. I DO NOT want to stay in academia any longer after my PhD.

Do you think this motivation will suffice to push through? Is there any chance that things will now change?
Maybe a happy relationship makes you too comfortable to pursue a PhD? It truly felt like I had 'settled down'. This city is where I would be staying for the rest of my life, and family plans were just around the corner. I imagine that this concept does not suit PhD studies.

I'm scared that a job in the industry will be no less frustrating. My worst fear is that all my passion for my field is just an illusion I've built for myself - and in reality I'm just too lazy to do hard work.

Also, whenever I read other PhD's talk about their work, it doesn't resonate with me at all. Things like constantly thinking about your research, and thinking "I should be writing! I should be writing!". Late nights in the office, races against deadlines. That all wasn't me. I somehow adapted to getting by with the minimum amount of work required. As a result, I have spent nearly a year without a publication. My life became totally empty and dissatisfying.
As a result, even my relationship ended. My girlfriend warned me multiple times that she could not stand my constant lamentation any longer. Two weeks ago, out of the blue, she broke up with me. I should have seen the warning signs months ago, but I didn't.
The very reason I sacrificed all my plans of the future is now gone. I'm in a city I wanted to leave years ago, doing work which I don't enjoy.
I always believed that I love my work, that I have an innate passion for what I do. It would have made perfect sense to go for a PhD, do something new out of my own volition. But that did not happen while I was in a happy relationship (at least it was happy for me), so why should anything change now?

[Continued..]

I'm facing multiple life issues; pondering the continuation of my PhD is a major part of that.

To give brief background, I have never intended to stay in academia as long as I did. After completing my BSc I thought I'd be off to the industry, working some dream job in the valley. It turned out that I was too scared to actually apply for anything, and I soon realized that the odds weren't exactly stacked in my favor. So, I thought to myself, continue doing a MSc and specialize on a narrow field. I struggeled tremendously with my master's thesis, loosing faith in myself.
Either way, by the time I finished my master's degree, my plans had changed. I was in a great relationship and convinced myself that I will probably be happier just staying where I am instead of giving it all up for a career and moving away.
At some point a really good PhD position had opened. The position is a very well paid, with secure funding for 3+ years, and lots of academic freedom.

However, I never really got into the work mode of a PhD student. I started out doing regular 9-to-5 like everyone else, but soon even that declined to less hours. I was extremely unhappy with being back at university, in a dirty office working mostly by myself. Worse, nothing creative has come to me. I always thought, if only I have a full-time position in which I can do anything I want, something *must* come out of it.

Also, whenever I read other PhD's talk about their work, it doesn't resonate with me at all. Things like constantly thinking about your research, and thinking "I should be writing! I should be writing!". Late nights in the office, races against deadlines. That all wasn't me. I somehow adapted to getting by with the minimum amount of work required. As a result, I have spent nearly a year without a publication. My life became totally empty and dissatisfying.

[Continued...]