<human>: I'll try to make this a quick read..

We've been in a relationship for a little over 3 years and dated for a bit before that. I'm not sure what category this would fall into but whenever I have anything to do with a person of the opposite sex,  she gets instantly mad and starts questioning me about the person and asks why I'm talking with them and tells me to stop. She won't allow me to add any new female friends on Facebook and says that I don't need to know any new girls.. 

And she completely freaks out when I touch any girl in anyway.. one time she even punched me in my stomach..

I'm fine with the fact that she doesn't want me getting any new female friends or that she doesn't want me talking to someone I don't already know.. or that I shouldn't be touching other girls (even though it's not inappropriate).

Now.. let's take a look at her. She has no problems talking with other guys, flirts with some of her male friends and others that she has just met.. and often in front of me. Doesn't have a problem with coming on contact with other guys.. there was a time where one of her male friends came to a party at the lake and she just literally jumped into his arms and wrapped her legs around him right in front of me.. like what..?

She finds it okay for her to do these things but freaks and gets angry whenever I have anything to do with any females...

Just today she went out to lunch with two of her male friends and it's fine by me but if I were to ever to go out for lunch or anything with my female friends, I know for a fact the she would flip the fuck out and tell me how I'm messed up and this and that...

Is this just a phase? Or what's going on? This is the only serious relationship I've ever been in so I don't know what to expect or what to do..

Summarize the given text in a few sentences.
<bot>: GF (21F) gets angry whenever I(21M) come in contact or have a conversation with another female but she finds it okay for her to the same things..