He fell for my sister?

My boyfriend(27yrs old) of 5 years recently broke up with me b/c he fell in love with my sister(17yrs old), she is 10 years younger than him, and he doesnt want to feel this way for her. he is disgusted by how he feels, and he doesn't know how to make it go away. he knows that she will never be with him. personally I think he is confused by their friendship, but I dont know. Is there a reason he move past this, do you have any advice as to what is going on in his mind?

After a year only three percent are still in love. If your sister will never be with him, he will probably soon loose his interest in her. He might come back to you when his infatuation for your sister wanes. But I understand if you are confused.

thanks for your reply. I know he'll get over her. but if his feelings disgust him because of his and her ages, why did he allow it to happen? there has to be something psychological about this. he says he still loves me and everything. personally, I love him too, but if things like this are going to keep happening because there is something wrong, psychologically, I dont want to continue with him. inside the male mind, I know they are. well most of them, are trying to have lots of women, my concern is why, of all people, why did he think about my sister? could it be he wants someone different, or does he want the younger me. my sister, looks just like me, but she is meaner. well more moody, is what I should say. where I would cry, she'd turn into a real witch. I used to be like her, but I grew up and learned to control my temper, other than that we are very much the same. I am just confused as to why my sister, when there is tons of other women in his life that he could've fell for. and personally, what would you do if this happened to you? It's like a soap opera. something you never think could happen. have you ever come across this situation?