He acts differently with me when we're alone than when we're with people. Is it normal or does it mean anything?

He acts differently with me when we're alone than when we're with people. Differently as in so much nicer, and almost flirty but not quite. We're sort of closer. We talk about things and then we stop when other people come. We get to know each other.

When we're with people, he's more distant but still talks to me in a teasing/friendly way.

PS: We're just friends, we share a class & we hang out together every day.
He acts differently with me when we're alone than when we're with people. Is it normal or does it mean anything?
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