Well done on reaching this milestone. I think there will always be times when we "think" of a cigarette. As long as it stays a fleeting thought we're safe. And that's why it's so important for us to realise that it can never be "just the one" or just one puff. As your friend learned, once a nicotine addict, always a nicotine addict. I hope that what he sees you doing will encourage him to quit again.
Stay free and stay enjoying it.
Teresa