My Little Sister Really Hates My Boyfriend. What Should I Do?

This is for advice. I'm 25 but my little sister is 14 and doozing on the internet. I've had tons of boyfriends that she's liked or at least tolerated. She does get very picky, but that's just a side effect of having a teenage girl in the house.<br><br>About a year ago, I met the most perfect man ever. He's 27. I was so smitten with him because he was so respectful. He was a US Marine. He's really clean and neat and organized. When we go to restaurants together, he always pays the bill but he does so in a way that makes me feel like I'm in control over whether or not he pays. He's just such a sweet man.<br><br>About a month ago, my life got really crazy and he moved in. So he's living in my house, and my 14 year old sister lives with me. She's a teenager and I want to make sure she's comfortable. So I asked her if she was okay with him, and said a bad thing happened and he had to go I'd support her. She said she was fine, no problem, he was nice enough.<br><br>But she doesn't like him. She hates him. I think she's acting bratty. She doesn't really have a good reason to hate him, she just does. Does anyone have advice on what I should do? She's starting to make my life really hard. As a boygirl I know women have a reason for their actions, but I have no idea what it is.