We were just talking about this! Remember those magazine spreads in the early 00s, about how to do this without looking matchy-matchy?
In public, we're rarely dressed at the same level of formality, sometimes comically so. In private, our loungewear coordinates but not intentionally; it's because of the preference for same colors that Celia mentions.
Weddings, we don't attend together because does the wedding couple really need to pay for hosting (and make space in their guest list for) whichever of us is the +1? We prefer to view those invitations as polite fiction and spend time with the couple together a few months later or whenever it works out geographically.