It may be good to clarify what you mean when you say you will only be comfortable as primary. Primary can mean different things to different people. In many circles, I hear primary used to mean a life partner (so if you are living together and married and maybe kids together you are already a primary), and secondary is used for serious relationships that do not plan to become live-in partners or life partners, and tertiary partners to be more of the casual (but maybe still loving and/or caring) relationships that stay on the periphery and might not last long or take up much of their time.
Even if you are using terms like primary, secondary, and tertiary, it is good to make sure you clearly define those terms. Once there, how serious is he allowed to get about other partners? I have two primaries. I live with both my boyfriend and my fiance right now. If you are a primary, are you okay with the presence of another primary? Or is primary a tier that only the two of you are going to ever have with each other?