Does my sister fancy my boyfriend and why is she copying me?

Anonymous
I'm 22 and my sister is 31, I have a boyfriend and she is single, and she has struggled to keep a boyfriend. Anyway we have always been very close since I got older, but recently I have noticed how self obsessed she has become and how everything has become competition between us. I have been with my boyfriend for 3 years and he is quite close to my family and gets on very well with my sister - which is great, but her behaviour has become slightly inappropriate for my liking as she would start making comments like 'I'm the prettier sister, I have the cuter face, I have a bigger bum'. My boyfriend really likes the Spanish look, which my sister knows, and she says he will fancy her more than me, as she looks more foreign because I am paler. When he stays over she says she wants to see him and they will have to have cuddles (they've never cuddled). She always 'jokingly flirts' with him and on my graduation they couldn't watch me accept my degree, so instead of being normal about it she said she was going to get him drunk and would make rude comments about him liking her. My sister had been staying over at mine bcos she wasn't feeling well, me and my boyfriend were on the train home and she starts sending me snaps of her in my room trying on my clothes in the mirror, and then she sends pics of her posing with my glasses on. I wasn't happy and so when I got home I expected her to be in her own clothes, but instead she comes downstairs with a small dressy top on and my tight flared pants. I didn't understand why at 3PM she was wearing a night out outfit that was mine. After that we went out me, my sister, my boyfriend & brother and as we were driving she said to me that I wudn't ever get a mortgage on a house, because I am a floater. So I asked what she meant by a floater and she said that I just float between things and don't commit. This really offended me as I have a full time job and I graduated from University last Summer.

Pls shed some light, why is she behaving like this?
Does my sister fancy my boyfriend and why is she copying me?
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