Give them as much as you can ... They can understand you as well as you want, even better than your parents, and even better than that boy or girl that you have ...
Love them as much as you would love them to be for you.
The point is that never overlook or hesitate to go to them in case of being wrong, or about to fall. Older or younger, immature or not, after all it's your brother ... And he can show you his love in his own way. Half of your being is him and vice versa ... So if you have a brother or sister, value them as much as you can, they will never leave your side, even if that's what life reflects.