I don't know if this is all real or not (every time the OP posts, it seems more and more fake...) but I'll tell you a true story, OP.
One of my best friends admitted to me that she and her cousin dated for 4 years secretly, from age 12-15, I think it was. No one suspected them. No one ever caught them. So what went wrong? Guilt. They both felt horrible guilt every time they were together. When their relationship became sexual, the guilt was even worse. They both cared for each other, but eventually the feelings of guilt and dirtyness overtook that. Now they avoid going to family reunions and parties because they don't want to see each other because it reminds them of their "sins".
And that's just her cousin. Imagine how disgusting YOU would eventually feel...with your BROTHER! You're already on a slippery slope just by holding hands at your ages. Don't ruin your life or your brother-sister relationship with your brother. Find a guy OUTSIDE the family.