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TLDR How do I tell my boss of ~9 months that I want to leave to run my own business?
I will start with a bit of (relevant) background to this question to give some context. I was a self employed web developer during university and was quite successful with my work.
When I finished university I got a job straight away via a recommendation from a client, it was remote and I did well in it for 18 months, I did miss self employment though. I then managed to land a job in my local area with much better pay but in an office.
At the interview, it seemed that I would be working with a couple of others but when I started work they were no longer there and it has just been my boss and I in the office ever since.
The first month or two at the new job were good but things have since gotten very stale. Being the sole developer at this place, I have to balance bug fixes on old company projects with creating new functionality for our new clients and I am not enjoying my time here at all. My boss (the director) is excellent, he is friendly and flexible and the pay is good, but I don't feel happy.
I feel now more than I ever have that I want to go back to being self employed, but full time. I have a number of contacts (from my past and unrelated to my current job) that want to use my services, some on a project basis, others on a monthly retainer basis. These are reliable enough to give me the confidence to go it alone, and I have been saving for a few months to give me a large buffer in case things go awry. The chance of getting work from my boss is relatively likely but I am obviously not going to count on that. My business is not in the same industry as his, so no threat of competition for him.
My main question is, how do I tell my boss that this is what I want to do? Being the only two people in the business at present make it feel harder for me to do. I want him to know it's not a personal thing but just something I feel I need to do but not sure how to do that succinctly. I'm looking to go in December, so would be giving my 30 day notice in November which is not far away now!