They're already thinking it

A: You’re unlike any other woman I’ve ever met. Move in with me.
B: Sean. No, it’s too soon. What will people think?
A: They’re already thinking it.
B: And I’m tired of lying. I’m tired of pretending.

Question: Is it okay to use the object “it” after “think” without any propositions?

Thank you!!!

Yes, if it refers back to something previously mentioned (which is the case here - the ‘it’ is the ‘what other people will think’).