I'm trying to do the same thing at the moment, OP. I don't know your social routine, but for me I find talking more to the other people in my circle helps - the person doesn't catch on that I'm not talking to them specifically , since I'm still there, in a sense. Subtly 'blanking' them means their not hurt by my sudden absence, or that I refuse to be around them... partly they're just too self-absorbed to notice little changes in their friends, but that helps! Course, the best way is just to let it happen naturally - find other friends, and things will go at their own pace. Your 'friend' won't be alerted to your intentions that way.
Thought he was 19... really he's 14