The trouble is that even when Peter is making an effort to take it slow -- and even with this place setting him at ease -- he's simply not very good at sex beyond chasing his own pleasure (though he does that quite well). It might come as a surprise to her, then, when the act is languid and sensual this time. It does him, insofar as he thinks about it rather than simply enjoying it (so not a lot). It's everything he wants from sex, everything real sex falls short of.