Hey bud. I think the biggest thing you need to learn and realize which is very hard in your early 20s, (I am 24, but have nee wanting to quit since 21), is that your reputation doesn't mean sh1t. You need not maintain some level of cool with anyone whose acts and habits are dangerous and disorderly. There is no such thing as being "manly." (Be a man, drink a beer). I am 24 living in a pretty crazy drinking city. Unfortunately, I am missing out on so many other beautiful things within my life just dealing with hangovers, loss of money, hanging with the wrong crowd, and so on. I am ditching some friends that drink....I left my girlfriend for many reasons, including her lack of support when I wanted to quit. It is time to clean house and find out what you want in your life.
You need to do what is best for you and your future. Do not try and make your brother happy by participating in drinking. If he truly loves you as his brother, he will accept that drinking is damaging in your life, and will push for you to get rid of it.
He needs to realize he can either:
a) lose his favorite drinking buddy, but gain a happy, loving brother
b) lose his favorite drinking buddy, and lose his brother forever.
Those are his choices, and anyone else whom supports a drinking version of you.
I hope that didn't sound too aggressive or forceful, but I was just trying to light a fire under ya! Good luck man!