You enjoy talking about X, and it makes you happy. It feels good to be with other people when you can talk about X. It would not feel good if everybody else just talk about Y and Z.
Other people like to talk about other things, and it makes them happy to talk about them with you. It makes them feel good around you and like to be with you.
Sometimes, remember to not only talk about X but spend some time asking what other people are interested in, and ask questions about it when they do talk.