What the **** is the deal?

Ok, amazing night last night and an amazing afternoon today with my girlfriend. I come home an' i get a load of nice texts an' whatnot but then i get one asking me not to talk to the people that are going to be coming into the 6th form because they're all bad slags and will try it on with me. I tried re assuring her but it doesn't work.
Now she's gone off in a little strop for some reason trying to tell me that i will talk to them all an' let them add me on facebook...

Before i got with her, a few of the lower years added me and one of them was a bit flirty. I deleted this one as i didn't want any suspicions to arise.
Now she's made up this scenario that it is really bad to let on to someone (just by giving a slight smile or nod) that had been a bit flirtatious when i had first got with her.
I really don't understand it because i got rid of a mate (girl) who i'd known for 3 years just because my girlfriend felt uncomfortable about it. While we're out, she talks to a shit load of lads who she used to know or has had things with and i can't even let on to someone... what the **** is that?

Anyone know what's going on?

Yes, you're engaged in a power struggle. Don't let her make rules for you she won't follow herself.

What d'you mean?

How can i combat this?

If she wants to get into a snit about you having female friends, she can get rid of all her male friends.