HELP!!! my sis is telling my parents everything thats happening between my boyfriend and me andi hate it!!!!?

ok my sis has been finding out stuff bout e and my boyfriend like private stuff -_- shes my only younger sis and when she tells him i always get in deep trouble and i disapoint him like i didnt tell him that i was cing my boyfriend this one time and said i broke a rule but he would've never known if my sis didnt tell him!!!! she getting on my nerves and same with my dad!!! now hes like 'ill give u 100 bux if u find out that they kissed' omg im so sick of it!!! and we aready kissed so im a lil scared 0_0 help what should i do!!! ive already slapped her and got in big trouble 4 that!!!!