Should I leave my PhD after 3 years with a Masters?
I might be the person you're looking for an answer from. I left my PhD program in 2016 and took my Master's with me into the job market. I do not regret this decision.

When I was an undergraduate, I looked at the PhD as the ultimate life challenge and the ultimate accomplishment. I wanted to prove to myself I could do it even more than I wanted to make a career out of the PhD. 

My first year of graduate school was shockingly hard. I struggled to adjust to the workload and I always felt dumber than my colleagues, even though they assured me they all felt the same. After a year, I adjusted, and even began to excel. I began to recognize the patterns of graduate school, and I developed a rhythm that helped me anticipate and overcome the major challenges.

After completing my Master's thesis, I started studying for the Qualifying Examinations. This was the period where I began to consider leaving the program altogether. Aside from one exam, the second half of the program was exactly identical to the first: I'd do a bit of traveling for research, I'd spend long hours writing my dissertation, and I'd continue to TA and run summer courses. 

At this point I was absolutely confident I could finish the PhD if I wanted to. I had already published three books (as a hobby, unrelated to academia), so I was certain I could complete the long-term project of dissertation writing. In fact, one night I counted out all of the pages of research I had written for articles and papers in the past two years, and the number totaled right around the average length of a doctoral dissertation in my field. Writing and research was not going to be a problem.

But completing the program would require another 3 years of my life, and I was already approaching my 30s. My fiancee had been working for years and had her career already built up. She was making real money while I was living off of TA stipends and begging random institutions for grant money. With my income, we weren't going to be able to have a family, buy a house, live the American dream, etc. Our lives were just on hold.

Then I began hearing the horror stories of PhDs struggling to find jobs. Every recent grad I knew, regardless of major, couldn't find work because our university wasn't a top 10. The only exception were the CS majors, who had no problem securing gainful employment. But my housemate, for example, a man who completed his Chemistry PhD by contributing to a new HIV drug, was unable to find a job for two years after he finished.

In the end I had to make a value judgment: was my pride worth my family's future? The answer was no. So I left. My advisor abandoned me (she won't even respond to my happy holiday emails that I occasionally send to my former professors) and some of the guys in my cohort probably considered me a washout. But I've got a happy marriage, a great job, and I'm buying a house within the next two years, so. I got what I wanted out of the experience, and I feel like I stopped at the right time.

I strongly recommend you prioritize your mental health above everything else in your life. Because if you don't have that, then you have nothing. All the money and job security in the world won't make you happy, and therapy might not put you back together. The thing about the PhD is that you have to be 1000% committed to that vision of your life. If you aren't really interested in research, and if you always feel in your heart that you don't want to be there...maybe you should listen.

Before you leave your program, consider taking a Leave of Absence, which is totally acceptable and common, especially for mental health-related reasons.  

edit:

One more question for you to answer for yourself: Is there any additional benefit to having the PhD instead of just the Master's? Usually the MS is plenty for landing a job in the corporate sector, and the PhD is if you want to do full-time research (which you obviously don't) or lecturing as a professor (which you didn't mention).