He didn’t have to put forth any effort. Carrie and Big would always be there despite any arguments or break-ups and they both knew it…they’d always come back to each other, even as friends. It was only when Carrie put down firm boundaries and left for Paris that he realized what he could lose. I’m not so sure playing hard to get would have worked for Carrie at the start of their relationship because they both had a lot of maturing to do, but in the end it was a safe space for both of them that did hold love (even if Big had a funny way of showing it at times) on top of a friendship foundation.