S.L.
C.,
What a sad situation. My heart broke for you when I read your post. As hard as it is, it is not our place to judge another's "spirituality". It's not your brother's place to judge your walk with the Lord and it's not your place to judge his. God is the only one with the authority to make this judgement.
Our pastor gave a sermon the other night that I wish you could have heard. He was talking about how God might call one person to one standard of living (guiding them to not listen to contemporary music, for example) but might allow someone else to live in greater freedom in the kind of music they listen to. We are not to place or try and force the standard He has set for us on anyone else. (If you'd like some scripture references, email me and I'd be happy to send some to you).
Remember that we, as Christians, are under God's grace. Under grace, the legalism of the Christian faith is removed. Jesus came to fulfill the law for us because we do not have the ability to do it on our own. We NEED His grace.
I can't tell you how to deal with your brother...honestly, I think you're just going to have to pray that God would work and soften his heart. I will be praying for you that you would not let your brother affect your walk with God. God is concerned with our hearts, that we reflect Him. I would encourage you to focus on that right now.
S.