All good advice. If this time doesn't start now I would agree to not date any NEW people during that time, but I would not stop seeing people I was already seeing, though I would agree to manage my dating schedule so that I had set dates and my availability to him was constant and known.
I don't consider new dating partners to be an emotional outlet in the context you are speaking of - you can choose to focus on making friends with the potential for future dating. You are reading as really pissed off to me, I am wondering if there have been other things Dan has done that you feel are "ridiculous" or if you just really aren't happy in this relationship and would be better with a poly partner who is also dating. Truth is you have a winner in a partner who recognizes their limitations and feelings and is asking ahead of time for what he needs instead of telling you its "fine" and then acting like a passive aggressive jerk later. Most people who post for advice on forums would be thrilled to have a partner willing to ask for what they want, and be asking for a limited time change instead of an open ended one.
Happiness will never come to those who fail to appreciate what they already have.