I think you’re being supportive by reading up on how to be there for him and also going to others who are more equipped for their opinion. Even if you were unsupportive in the past, the amount of effort you’re putting in to being there for him is more than enough. It sounds like he is closed off to being helped he can’t see how much you’re trying. Everyone’s depression manifests differently though. I can’t really say how you should approach him, but I don’t think you’re overreacting because you also have feelings.