She has a boyfriend, but she seems to get jealous when other girls talk to me why?

Well as in the title she has a boyfriend, I try my very best to be respectful towards that and respect her boundaries. But I’ve noticed with her every time another girl talks to me she seems to get jealous? I started to notice this one day when, she was talking about her boyfriend in front of me. But once I started talking about another girl who I was talking too, she became disinterested and quiet and was trying to get out of our conversation. she would just say, yeah yeah and giving me the 😕 kinda look. Since then I’ve noticed as well she’d see me and just wave saying “hey how are you?” (I know that means nothing lol) however if she sees me talking to another she she seems to put herself into our conversation. And being super friendly and talkative towards me more than she usually is. Now anytime we are talking she’s always giving me little comments like saying “you’re such a nice person” and catching her from the across the room giving me big smiles. Any advice would be greatly appreciated thank you 😊

She has a boyfriend, but she seems to get jealous when other girls talk to me why?
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