How do i stop her?

ok well me and this girl are going out for the past month all is great till she starts going out for a drive with her new friends. i get corious as she wont introduce me to them and that she trys to keep me away from them i find out that 1 is single and fancies her which makes me wonder i told her he fancies her and she turns on me. now she canceled mspending all sunday with me and instead gives me 2 hours then ssays she is going out with her 2 mates 1 has a girl the other fancies her then starts fobbing me that she has to drive with the single one as the other will have his girl there it turns out that the other couple didnt turn up.... so i ignore this and today she cancelled meetin me 10 mins before meetin me to go to this single guys house for a drink and then i see her in his jumper walkin beside him i txt her she gets annoyed calls me a and says that they are heading to a friends my mate offered her a lift and they said no