Am i just a jealous girlfriend or does she really like him?

Okay so my boyfriend knew each other from a friend. She goes by "Chey" and so now that me and my boyfriend have been going out for quite some time now, she somehow finds a way to get in between us. For example, she goes to his house to talk to his grandma without him even noticing. I dunno if she's trying to kiss ***...but it's sure working. And when we were all hanging out in a big circle and laughing cuz it was at brunch. She has to mope and get all depressed and then my guy asks her what's wrong and stuff. She tends to be closer to him when they stand...Then they start talking. He's really friendly to everyone which is why he had a lot of friends when he moved here. Anyway, do you think I'm jealous or she likes him?