I signal less and am less social overall when in a serious relationship.

Oddly enough, that's part of what I'm talking about.

Outside of a relationship, the immediate, hedonic stakes are higher in any social interaction (for you apparently, and also for me -- I don't mean to speak for/about any others). The other party can sense this, and it makes you seem low-status. If the interaction seems less intrinsically important to you -- if you're not going to take a large hedonic hit depending on how the conversation goes -- this makes you seem more high-status.

(HT: Eliezer, who articulated the distinction between hedonically valuing social approval and valuing it for its utility during a panel at the Singularity Summit)