This is so unfair i cant even believe it?

ok, here's what happened. i spent the nite at my friend Zoeys house last nite and one of our other friends, Rachel, called a little bit after 1am and asked us if we would help her get outta her dads house. her parents are divorced and her dad is really abusive to her and stuff. well i guess her dad had been drinking and she was scared so she asked us to come get her. Zoeys parents were sleeping so we snuck out and had to walk to get her since we arent old enough to drive. once we got her out of her dads house we started walking back home. we saw a car drive by and then it stopped and backed up. it was my brother Kris and his girlfriend coming home from being out. sigh. he made us get in the car and he drove rachel home to her moms and took me and Zoey back to Zoeys house so he could talk to her parents about what happened and i could get my stuff. i live with my brother and he is my legal guardian. once we got home i totally got yelled at for sneaking out of my friends house and being out that late. i tried to explain to him that the only reason i even did it was so Rachels dad didnt beat her up. but he still was mad and he grounded me! i dont know for how long cuz when he gounds me he never tells me how long its for. and tomorrow is my best friends birthday party and im not allowed to go! she wont understand why im not there, we're that close. i told her im grounded and she cried! Kris(my brother) did say that he would drive me over AFTER the party to drop off her gift but that is it. i just dont see why im grounded or trying to do the right thing and help my friend out. do you think he will see it from my way and maybe let up a bit? isnt it unfair?