Mal isn't even sure it is happening at all. He's had enough dreams that went more or less exactly this way to believe it perfectly feasible that this is just another one. Maybe the mudder's milk knocked him out, and this is all some kind of hallucination? There doesn't seem to be any other logical explanation for why Inara wouldn't have pushed him away by now, or hell-- even slapped him, as opposed to kissing him back, like she wants this just as much as he does.

He can't remember exactly when he fell in love with her, but it was a very long time ago. He's scared too, though not for the same reasons. What scares him is the thought that any second he'll wake up and she-- this amazing woman-- will realize she's kissing Malcolm Reynolds and pull away, that she'll regret it, and reject him. He puts his arms around her and draws her closer as if to combat this fear, his heart pumping, it seemed, almost audibly.