Why was he tracing my lips with his finger?

So my now ex boyfriend came out as a transgender and wants to become a woman, that's why we broke up but we're still very good friends. I help him with make up and clothes so he spends night at my place.
Usually he touches my hands or head but this time we were watching a movie and all of sudden he started tracing my lips with his finger. He said it's nothing but I wonder ehy he did that?
Why was he tracing my lips with his finger?
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