Secretly Working a Side Hustle while working a Full Time Job

I’ve been working my day job which pays me a lot of money, at the same time I’ve been cheating on the job by working to build my side hustle. Long story short I want to make enough to work for myself but the side hustle doesn’t pay the bills yet.

I’ve been having some conflict with my day job boss where he is stepping on my toes and micro managing my job. I think he likes to be overly involved but he is an engineer and I’m in sales and he made a critical error with a customer – in any event he wanted to strategize on it and it’s Saturday and I told him I’d like to talk about it Monday and asked he not reach out to the customer again with a sales matter until we talk as his communication with the customer opened the door for a problem. He wrote back upset with my comment even though I tried to be as diplomatic as possible.

If I was working this job and not “cheating” building the side hustle on his company time, I probably wouldn’t have allowed this to happen. But, I’m reluctant to challenge him because I need this job, I have guilt for not being 100% present in it, and, lastly, he doesn’t take advice/criticism well, he’s kind of the type that is moody and gets pissy if you call him out. When he wrote back on a Saturday via email that he wasn’t happy with my comment I did not want to reply because it would be a pissing contest on my personal time but I feel stressed having to face him to discuss this further on Monday. Looking for any and all advice. Thanks.