The speaker is talking to a former partner, and the poem reads like the first shaky steps after a breakup. They are smiling but admit they don't quite know why. The best guess they offer is freedom: they can finally do whatever they want, even if they haven't figured out what that is yet. The only thing they're sure of is that it won't include the ex.
The tone shifts as the poem goes on. At first it feels light and relieved, but small digs creep in. The speaker points out that the ex's friends are their friends too, as if staking a claim. Then comes the sharpest moment, when they say they'll soon be with someone new and wonder how the ex will feel watching it. The last line, "The way you never will again," lands like a closing door. The mood is a mix of relief, defiance and lingering hurt, suggesting that the speaker's confidence is partly a performance and the smile may be covering something more complicated.