"What we've got here, is failure to communicate"
Sounds like, at the very least, there are some conversations happening that not everyone is involved in (or possibly not everyone is listening).
If the relationship was previously open and has been subsequently closed this is something that needs to be discussed unambiguously. If his assumption is that your dating tendencies are dictated by his, this is something that should be discussed WAY out in front.
Either way, you two would do well to sit down and have a conversation, one that is not filled with assumptions, hinting, and hoping. Even if you decide to end this relationship because it is dysfunctional (and that might be the best response) you will still need to keep in mind for future relationships that this was caused by poor communication ... by everyone involved.