Does going to a social dance together mean staying partners all evening?

A dancer asked me to join the next song. Before I could answer, the friend I'd arrived with said, 'We're dancing together tonight.'

We're friends, not a couple. We'd taken six weeks of beginner classes and decided to try an evening social. I wanted to practise with different people. He wanted a familiar partner while he found his feet. Neither of us had said that before buying tickets.

I stayed with him for the song, then told him I'd like to accept other invitations too. He said coming together should mean not leaving the other person standing by the chairs. I offered to alternate a few songs, but he thought that sounded like allocating time to him.

I enjoy dancing with him. How do we agree on what arriving together means without making me responsible for every song he doesn't dance?