The other problem is that my secondary relationship is totally hidden. My primary and i are well known in our area and 95% of people we know think we are the perfect monogamous couple and for his career it's better that way.
I understand the need to keep your relationship private. But you're allowed to have friends, right? So you ask your mutual friends what they think of Secondary as a person, "because you're friends with him and your Primary has concerns about that, and you want to know if they're justified."
I would add that you insist your primary tell you who is saying these things. Tell him that given the circumstances, his word is not enough, and that you believe he's making them up to sabotage your relationship.
Keeping in mind that your friends believe Secondary is just a friend, there's no good reason for them to keep it a secret from you if they think he's bad news. And if he's so rotten, why are they friends with him?
Basically, you have to refuse to believe him, and make it clear that you're not going to tolerate his poisonous behaviour.
My primary sees him as desperate not b/c i'm not good enough but b/c i'm soooo good that he will take whatever he can get with me, ie sharing me. He feels weak and less of a man that his woman is out galavanting with other men while he sits at home alone
Ahh, gotchya. So in other words, classic insecurity. He's afraid that you're going to leave him, and the only way he can see to prevent that is to spoil it for you. Which means, whether he intends it or not, he'll spoil it for you no matter who the other guy is.
This definitely has nothing to do with the other guy, it's all about your primary. Since I don't know him, I don't know the approach to take. But the result is you need to make him see that his objection is not to this particular other man, it's an objection to your lifestyle in general. That he needs to deal with his feelings about what you're doing from his own perspective, how it relates to his life, rather than projecting it onto the other man.
He also needs to understand that even if he's successful in driving away the other guy, it will only cause you to become resentful and that you will later get together with someone different and the cycle will repeat. That you're not poly just because you met this other guy, and driving away this other guy won't make you stop being poly.