<human>: My bestfriend has been dating this guy for 4 months and ever since she's started dating him she's been acting different. She prioritizes spending time with him over me, and she is extremely possessive of him. I said a joke asking him about their sex life and she got all pissed at me and said how disrespectful saying it was, after I repeatedly apologized and said it was just meant as a joke. And we have some mutual friends and once she wasn't there but he was, we playing this truth or dare-like game and I asked if he wasn't dating her would he hook up with me, and she found out about that and she was absolutely furious at me, she takes everything literally and thinks that I'm trying to steal him from her. She takes the most insignificant things and makes them out to be the end of the world, she is like a textbook jealous controlling girlfriend, once when I hugged him goodbye I grabbed his butt just to be funny and she literally grabbed my wrist and started twisting it around and said I'm sexually harassing him and she just can't take a joke at all and this is causing a lot of tension. How do I deal with her being like this? Is she being unreasonable?

Could you distill the essence of the text into 1-3 sentences?
<bot>: My friend has been dating this guy for a 4 months and she is really possessive of him and gets angry at me for anything she perceives as flirting or sexual.