coming out about self injury?

[proudmacchick]

I started cutting about a year ago, and from the beginning, I know my boss suspected. (FYI, I work at a small, relaxed environment restaurant.) We had a short talk about it several months ago and I used the cat excuse. I doubt he believed me, but he hasn't asked any further. The info I have read on other sites deal with coming out to people who have little or no idea about SI. My boss, however, has read up on SI and has worked with people who have done it. Now I'm actually ready to tell him the truth, but I don't know what to say, or even how to initiate the conversation. The idea of telling him makes me nervous, but he needs to know the truth.
Any advice would be greatly appreciated.
actually, my boss and I are friends. He's like a second dad to me.