He can feel it, and for a moment he considers trying to get her to warm to him, trying to draw her in, but then he sits back on his heels. She's just given birth, she's probably tired, it would make sense for her not to be interested.
Admittedly this seems like more than a disinterest in sex; it's somehow deeper, a disinterest in him, in them, in where they are; but Alex is hoping that if he just does everything right things will go back to normal.