Just... eh, I don't know. Not too good, I guess.
My brother is roughly 2 years younger than me, and when we were still living together as a family we fought constantly, sometimes rather violently. Time and distance between us has helped improve our relationship somewhat, and we're more relaxed and even friendly to each other when we meet (which is about two or three times a year).
However, I also deeply resent him for being a horribly irresponsible, unreliable twat. He's been an on-and-off druggie for 8 years now, meddling in things that go way past pot and the like, and he can't seem to clean up his act. It continues to be a major stressor for our dad, and that's probably what I hate most about this mess; the man is 75, and raging and worrying about my brother's habit is going to put him in the grave one of these days. It doesn't help that my brother's always unavailable because he doesn't have a phone (landline or mobile), and he doesn't call for weeks on end, contributing further to the bad blood between him and dad.
It's tragic, really. My brother is such a clever guy, capable of achieving greatness when he actually gets of his ass to combine his natural talents with hard work and discipline, but instead he keeps teetering on the edge, continually wasting his enormous potential. It's frustrating and aggravating beyond measure.
By the way, if half-siblings are included on the list, things look better on that front.
I have a half-brother and half-sister from our dad's first marriage (they're 50 and 47 respectively), and I love them both to bits. Seeing how we all live hundreds of kilometres apart I don't get to see them often, but when we do get together it's always good times.