Did he actually tell you he has a primary and you would only have to be secondary? Or are you assuming that the other person he is with is a primary? Because that may not be the case - he may not use a hierarchy.
Some other things to consider: you might find that you can still see him as much as you want to, whether you are labeling your role in his life as primary, secondary, or whatever. It's not the label that's important, really. What matters is asking for what you want or need and seeing if he is able to fulfill those needs/wants and meet your requests. If you say, "I want to see you four times a week and communicate with you daily," and he is able to do that, what does it matter what superficial title he or anyone else gives you?
Basically, what you need to do is start asking him as many questions about how he incorporates polyamory into his life. Questions like: How many partners does he have? Does he have a primary who comes first? How much time does he have to devote to you? Does he have any rules or boundaries with his other relationships that will affect you? Do any of his other partners have "veto power" (the ability to nix you as a partner for him, for whatever reasons)? What safer sex practices does he use? What does safer sex mean to him? Is he fluid-bonded (having unprotected sex) with anyone? How often does he get tested for STDs? Make sure that, if you are confused by any of his answers, you ask him to clarify.
Also figure out what your personal boundaries are and let him know what you will and will not accept. If it looks like it's going to be a cool arrangement that you'd feel comfy with - then, great! If it seems like you will just have a whole lot of unmet needs, drama, and angst ahead of you then start pulling back emotionally and realize he may not be a good match for you.
Last edited by nycindie; 11-08-2012 at 06:09 PM.