The speaker is looking up at a grey, overcast sky and wondering whether their smile will ever come back. It's a quiet admission of sadness, made all the more striking because the speaker is surrounded by friends. They join in the games, but only as an act: "I pretend." The play is a performance, not something they actually feel.
The last phrase, "I sway into solitude," is the heart of the poem. "Sway" suggests a slow, almost unnoticed drift, as if the speaker isn't choosing to withdraw but is being carried away from the group while still standing among them. The gloomy sky mirrors that mood, heavy and colourless.
The overall feeling is lonely and subdued. There's no dramatic outburst, just a tired, private ache. The poem suggests how it can be possible to be in company and still feel completely alone, and how hard it can be to say so out loud.