Execution of ideas is a big factor...just because someone knows about your idea doesn't mean they can or will do a thing about it.

And even if they do, will they have the energy and ability to execute it as well as you?

You have two choices as I see it:

1. Embrace the public connection between you and the new business ("Yes! It's ME!")

or

2. Keep hidden behind the business name. Center all marketing around the business and downplay personalities. Use your first name only as much as you can ("Derek at JingoText").

Sooner or later your employer is going to find out.

You really don't have any control over what he does. Whether he's angry, supportive or ambivalent, you need to be clear with yourself about what you're doing and why.

How much do you value your business?

If being safe (which is an illusion: your job can be taken away at any time) is more important to you than developing your own business, perhaps you should turn the idea off.

Being self-employed takes guts. And you learn those guts while you do it--I can tell you from my own experience that I am much braver about taking risks, depending on my own efforts for income, and being my own boss, now than I was four years ago. So you don't have to "feel it" 100% at the beginning.

But you should know whether you're committed or not. And if you are committed, then it doesn't matter what your current boss thinks.