I think centering the song around "chocolate" is meant to be more than just a sexual thing. Chocolate is most commonly used as a comfort food--when people feel bad, they eat chocolate--it's comforting and reassuring, it makes them feel better. Throughout the song Kylie talks about how her prior relationships/experiences have not been good--leading to heartbreak and making her pessimistic. Yet, despite her initial reservations about this new relationship it has turned out to be a genuine love. She didn't go into it expecting much, but she realizes she has actually gained a lot from it ("an empty bet and still I won the cash"). Her love is finally returned, he knows her very well, she can depend on him, etc. It's all very comforting, like chocolate.
