Why does she support only him?

Im 26, my brother is 23 and my sister is 19. Me and my brother play kickboxing and there are times when we fight each other. In most of the games upto now I have won only 2 out of 16 games against him. Once he defeated me even though I had the help of my friend. The big problem is, my sister cheers and supports only him when we are on the ring. Naturally she is more closer to him than to me so sometimes I even feel jealous about her closeness to him. Last night there was a competition and as usual he won the game and I was disappointed and went home to meet with more disappointment as he was celebrating the victory with my sister and her friends. I kept quiet and later in the night I saw my brother lovingly maging my sister's feet which is a daily scene at home. Although I like to do the same thing,she has never asked me to do so. I feel bad about this and I have thought of quitting these games altogether and make him the champion for the first quarter.What do you think about this?