Well, if I was in your gentleman caller's shoes, I would like to know if poly was a possibility for you, even if you have not acted on it. As the relationship is quite new, I don't know if you need to bring it up immediately. However, as things evolve and get more serious (if they do), it should be put on the table.
P.S. Geeked out I got to use 'gentleman caller' in a post!