If I was going to build a robot...

Watched a movie, "Hot Bot", about a sex doll robot. Lately, watching things like that has led to distracting thoughts about how I would go about building a piece of software that, at least linguistically, behaves like a person in a particular environment (a narrow world). What is surprising is that this thought even crosses my mind. With working theories of language at hand, I sense that a great deal of the "intelligence" in conversation is already embodied in the word knowledge - per the word trees and structured relations that I know how to define. And I think it gets me close enough to have the thought cross my mind and wonder: what else I need in order to create a chatbot that can, itself, fall in love (as in the movie)? I am wondering how software should model "pain"?