Its not ok to feel this way  
So I have this like, little fan fiction in my mind of the CMC grown up. Their old classmates start having coltfriends and marefriends, so Sweetie Belle and Applebloom start searching for a coltfriend for themselves. Then one night during a sleep over at Sweetie Belles house, they start talking about boys and Sweetie Belle points out how handsome and sexy Big Macintosh is. While Applebloom feels awkward at first for talking about her brother like that, then she starts looking at him from a different perspective, thinking he was indeed handsome and well shaped and she also lived with him. So ever since she starts sort of stalking him wherever he goes and whatever he does and eventually grows a little obsession with him.  
But dont worry, shell snap out of it eventually. Its just a phase~