My best friend got annoyed at me meeting a guy friend for coffee

I met with a friend yesterday for coffee, because he made me a drawing, and he wanted to hand it to me, but also to meet me, cuz we're only friends online and never met. I kiiiiinda have a crush on him too. Small one.

No big deal, right ?
Not for my best friend.

First when I told her I won't sit for her to go home on Tuesday to meet the friend, she was like '' Are seriously abandoning me for this guy ? Come on who cares ? ''.

Then when I left, she told another friend how she didn't want me to meet this guy, cuz she thinks it's not right.

And at the end of the day, when I was about to tell her about my day with him, she was like '' Yeah good for you, I don't care anyways ''.

And today when I showed her the drawing he made, which is a total masterpiece, she only glanced at it annoyingly.

What the heck is wrong with her ? maybe she's being possessive ? She isn't this kind of person but well...
And no, she doesn't know the guy from anywhere...