A bit of background: I have worked at my current company for just over 3 years. I've been a manager for a little over 2 years. We're a small agency of 5 people, and I wear MANY hats and am the only one who knows how to do numerous important tasks. As a side hustle, I've been focused on growing my own business, which my company knows about. In fact, I'm the photographer for our clients on top of having my own photography business. Things with my business have begun to fall into place this year while things at my 9-5 are falling apart.
I am overworked and only make $50K a year. I have anxiety every day, need to get high to fall asleep most nights, am gaining weight, no longer enjoy things I used to, and generally dread my work days. It came to the point about 3 weeks ago where I was ready to quit and finally focus on my business full-time. My 3-year review was scheduled, and I planned to do it then, but it got postponed.
And then my boss was out of the office for about 2 weeks due to personal reasons, so I could not give my notice. My boss finally came back this past Monday, and that is when another employee gave their two weeks. So now, our team of 5 is going to be a team of 4 very overworked individuals struggling to complete the other employee's tasks while we work on hiring someone else.
At this point, I don't know how to leave my job without completely screwing the company over. The timing is awful, and since I'm the only one who knows how to do numerous tasks, I'll be putting the company in a difficult situation. For this reason, my plan has been to give 6 weeks' notice so I can train people on different tasks and also help fill my role. Also, my hope is that the business will still want to hire me as a photographer (as a freelancer, not as an employee), which is why I don't want to burn bridges. I feel horrible for wanting to leave and wonder if I should hold off on putting in my notice. However, my mental health is depleting by the day and I don't know how much longer I can do this.
tl;dr how do I gracefully leave my job at a 5-person company when another person just put in their 2 weeks?