Covert stutterers are pretty common. I personally can't handle it. It's just a bad way to live. I've found that people are mostly understanding, and if they're not, then they're not the kind of people I want to be around anyway, so fuck em. As for having existing friends who aren't aware and that being awkward, maybe just start small, with one or two of your closer friends, that way you can explain the 'covert' part and they'll be more likely to understand.