My fiance is too close with his sister!

I am 21 and fiancé is 21 and his sister is 23. We all live together because he refuses to move out with me, since he is worried about her. His response is always: "well what about my sister?" She is 23, not a kid anymore she can live on her own right? wrong. He has no problems breaking plans with me to hang out with her but he would never dream of upsetting his sister and cancelling plans with her for me, that is not going to happen. For example: We had a dinner date on Friday that we had planned a week before. She was suppose to go hang out with her dad that evening but her dads girlfriend had planned something for them so he told her he couldn't hang out. My boyfriend cancelled our date right away to watch a movie with his sister because he felt bad about their dad having other plans. Also he never listens to me. I can spend an hour lecturing him on something he should or shouldn't do but his sister can come along and say the same thing I do and he listens right away! Another example: My boyfriend got a concussion from a karate tournament. He was suppose to teach karate classes that night and I begged him to stay home and that it is not safe for him to engage in so much physical activity right away. He denied saying he was fine and absolutely had to go. As he is getting ready to leave his sister looks at him and says: " what are you doing? you need to stay home" He right away says : "okay yea" I don't understand, they hug for lond periods of time, he listens to every problem she has, we cant make noise because she goes to ved at 8pm, cant use the hair dryer because it will disturb her. But its okay for her to run the vaccum and nlender at 7am on a Saturday when I am sleeping... Ive tried numerous times to talk about it with him but he gets all defensive What can I possibly do?

Yeah - sister, not kid. Particularly as she's not even his younger sister. "He has no problems breaking plans with me to hang out with her but he would never dream of upsetting his sister and cancelling plans with her for me, that is not going to happen." It's taking sibling loyalty TOO far when it excludes ones ability to share loyalty with those whom status dictates deserve to be FIRST in line! Well, he can marry his sister, then, can't he, considering he's behaving more like her fiance than yours. Let's hope she makes him very happy. But in actual fact, I'd say, treating her more as if she's his MOTHER (think about it)! Otherwise, YOU can't make him change. You can only give him incentive to want to do so himself. Since trying to talk it through has failed, it's ultimatum time. And I don't mean 'her or me' because that's not going to happen. I mean, couples counselling or the puppy (our relationship) gets it. But make sure that gun is actually loaded or he'll firmly conclude it's just a toy one.