Puzzled as to why *mild spoilers*

Why was Heather so surprised by Leonard's wanting her after they slept together?

I get that she wanted to *revive* him (mostly for her own purposes).
And being young, she undoubtedly thought some hot young tail would perk him up.

But she knew how "old-school" Leonard was, how deeply he felt emotions.
Why was she so surprised that he took their sex seriously?!



I'd say this cloud is Cumulo Nimbus.
Didn't he discover America?
Penfold, shush.