What are signs that boyfriend likes your sister?

SandraBeex
We've been dating for a month now. I'm his first girlfriend. He's sweet and a gentleman. When we saw my sister, he said she looks older than me (im older). Whenever she's around like at school, he would mess with her saying "ZOMBIES" because she's scared of zombies from a movie we watched. He wants to come over to my house (really badly, kinda begs) which I feel he just wants to see my sister.

Me and my sister are complete opposite. She looks sort of like me except thicker. I feel like he likes her. I'm not sure if I'm just over thinking even though I over think a lot or it is true. I think she's prettier than me. Yesterday, afterschool, she came to me and he got his phone and was trying to take a picture of her I don't know but he started laughing and she walked away. He showed me and it was blurry and was the ground.

He has our homecoming picture as his wallpaper/background for his phone but still...idk if I'm just over thinking because I'm insecure or something or he really does like her and dating me because he wants to get closer to her. Also wanting to go to my house only to see her...
What are signs that boyfriend likes your sister?
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