Do you think he likes me?

During summer vacation, I went to one of my best friend's house. Her brother was home too, and apparently they arent supposed to go pout alone, so the three of us went to hang out w/ some of his friends. We had pizza, (all of us), and when we came back played a board game. While playing, i had my phone on the floor and he put his number in. When I asked him why he said "I dont Know" So we've txted each other a little. I think i might be liking him but find it wierd because his sis is my best friend. Also , when I mention another guy he always asks me who he is. Do you think he likes me?