The wife and I are monogamous. Being bi, of course I'm still attracted to the same sex, but that is not an avenue open to me in this relationship.
Outside of our relationship (before, after, and during separation), while I was dating or seeing other people, I assumed an expectation that the person I was seeing and I were free to see other people, unless specified. I think it takes a healthy self of steam to be able to handle that, though. I have been in situations where it was not spoken and one of the parties felt slighted.
But in general I am a relationship-type person. I like being exclusive with one person. I don't think I could handle an open relationship.