Do married gay couples take the same surname or keep their own?

They both take the surname "Ganymede."

Gay or straight .. what's proper is what the couple chooses to do.

I always thought this myself and even before I dated men. Regardless of gender, I’m totally open if you kept your name or hyphenated it. My last name will die off, and it is sad. My paternal lineage in America is 4 centuries old and my brother is also childless, so us 2 are really throwing it away so to speak.

What’s in a name? that which we call a rose

By any other name would smell as sweet;

R3 I would feel badly about that too. Glad my brother had two sons and they are straight and one just got married. Hopefully they'll keep the line going. I kept my name and my husband kept his. If I hated my family or was estranged, I might have chanted or combined our last names.

I know two gay couples where one person's surname was used for both. I know one couple that combined their names.

All the other couples I know kept their own last names. Those with kids either took one parent's last name or have hyphenated last names.

Yes.

Around 1900, it became traditional for women who got married to change their middle initial to the initial of their maiden name. I find this almost universal among female relatives of mine for several decades when doing genealogy searches. Then in the 70s when it became something of a thing for women to keep their own surname (maiden name) after marriage, one began not seeing this initial change as much among women who took their husband's name.

Out of all of my gay, married friends, the men all kept their own names. The lesbian couple created a new last name, and their previous surnames became their middle names.