I have my sister living with me temporarily. Since moving in she has become extremely close to my Husband. She talks to him about everything there is a problem with, stays up late with him. Yesterday (Christmas day) she wanted to sit next to him at the table, she ended up sitting opposite. Then she insisted on going with him to collect my other siblings from my dads (they're young). She wore the most revealing shortest dress and when they came back they had an inside joke going on that i still don't know. We then went back to my other sisters house for tea and she immediately sat right beside my husband on the sofa so I couldn't get anywhere near him. Then when he was talking to me she was trying to get his attention by showing him videos etc. When we got home we was going to watch the polar express as it's one of our favourite Christmas films but she suggested they play fifa 21 (I got it for him for Christmas) so they sat there and played the game. Meanwhile I was tidying up all the mess and putting our child's toys back together ready for this morning. I'm not sure what to do in all honesty as it's been going on for a few days now. I barely spoke to my husband yesterday and due to his work it was our first Christmas together. What would you do?