In a way, yes... it is easier to talk to people that are not involved in your situation than is it to talk with people who are emotionally biased. One of the reasons is to get a fresh angle, right? Like you're doing here. Another reason is, he probably doesn't want to feel like he is burdening you with information, or wants to keep his illness out of your relationship. I feel the same way in a relationship, I know that the depression is not really ME, nor is the mania, nor is the hallucinations, etc. I don't really want to share that with a partner, because I don't feel like that's who I am. It sounds like he loves you, and you obviously love him. Give him some time. it sounds like he's going through a lot of stress right now. You want to know what's going on in his head, because you love him. Have you told him that it's hard for you to just stand by and watch him go through this, and YOU would feel better if he could talk to you about it? Maybe if he recognizes the pain that is causing you, he will open up a bit, or at least tell you his reasons for not confiding right now.
You certainly shouldn't feel guilty for needing to unload, or feeling overwhelmed. I don't know why he would say that to you, it's not a very caring thing to say.
He is not treating you very well right now. Are you sure you want to put your self through this? I know you really care about him, but he seems unwilling to help him self right now, and you can't really help him in that state. Maybe if you back off, he'll realize what he's missing, and that he's made a mistake. Sometimes people need a little wake up call like that. All this time it seems you've been chasing him. Give him a chance to chase you, and you'll get your answer.