honetly i wish if i ask the same - the answer will be the same, in reality i won't get that. The response of you brother look like a response from someone who knows stuff about life and someone who cares. When there is no obvious reason for depression it's most common to be a chemical disbalance. At leasts that's my case. So trying new things, making changes, even if it's hard, is something to be done for real, no matter how hard it looks or get. You brother might not speak often to you, but honestly i think he cares about you, and most imporatnly he knows what to say in order to give that help. Sadly depression is something a person should take care by himself, others can't just wash it out. Also i don't think that looking into the past and specifically finding someone to blame is going to fix anything. The only real cure for life is said on Johny walker - "keep walking", it's not easy to do, but it's the real recipe.
If i'm wrong and your brother's response is just response, without emphaty and understanding, than i do have a big problem with relatives. Again that response is something i can only dream about if i needed to ask for help.