HMM. Have you talked to her? TBH if 2 guys kissed my gf I would be fucking mad too.
Just explain to her how much you love her and tell her that the other girls dont mean shit, all u want is her blah blah, buy flowers or something.
Dont nag about sex. Nagging is the worst u can do.
Me and gf didnt sex for 2 months, then i stopped caring. and then it was back to normal