Here's the context:
I'm a Software Engineer at one of the most elite companies in the world, I've been in the industry for five years, having worked on numerous projects, ranging from small to very large in scope. I've had the chance to dabble into some really new and exciting, bleeding edge technologies.
On paper, my resume looks great! I have five years experience, worked with lots of different technologies and languages, and I graduated from a respected university. Recruiters from prestigious companies, large and small always contact me. I'm on top of the world, and living the American dream!
Or so I thought I would be...when I was much younger and naive. The sad dark truth is: I've been dealing with severe depression for the majority of my life. I smile, I laugh, I feel great around people, but at the end of the day, deep in my core, I'm not happy.
Here's the problem I'm facing now:
The last company I had worked for, I got along really well with my coworkers. A great group of people. Gregarious, easy going, and generally very fun to work with. However, I moved on for other purposes, in order to explore new opportunities to grow my career.
I've been recently reconnected with a previous boss of mine, who I really respect and enjoyed work with him in the past. We've got along well, and he's always had a good impression of me. He's been asking me to join his start up for some time now. But now, he's really pressing for it becuase he needs me. Logically thinking, I would join him right now at the blink of an eye, but my depression has gotten a whole lot worse. If I were to join him, I wouldn't be able to perform to the standard that he has of me. I've been given multiple offers from other companies, but frankly, I'm not emotionally stable to join any other company even though it's the best for me career wise.
I've put his offer off for too long now, and I don't want to tarnish this relationship with my past boss, I just don't really know how to effectively communicate this to him without seeming or appearing weak or disrespectful. I always had mentioned that I'd like to continue working at my current company for X amount of time to think things through. But I've delayed this for too long. What can I do?