Ever since he learned to properly connect with it, the Force has felt more real to Obi-Wan than things he physically touches or sees. He shouldn't be surprised that translates to this.
It doesn't feel like a normal kiss when Qui-Gon's intangible lips glide over his; it's so much better. The part of Obi-Wan that is the Force feels like it's also part of Qui-Gon, so he experiences the almost-touch as a deep melding. He feels in that moment like a ghost himself, existing beyond the constraints of reality.
His many upcoming years of isolation suddenly don't seem so lonely.