Is it normal that im obsessed with my boyfriends sister

Okay so this happened about two weeks ago... my boyfriend was drunk on jack daniels and he fell asleep.. i went to get a glass of vodka and his sister grabbed my boobs and i just couldnt help myself... i've never done anything lesbian in the past but i couldnt help myself... i kissed her and we had sex right on the floor... i woke up in bed next to her the next morning and i felt so ashamed... but the thing is that now i think im falling in love with her... jack (my bf) is so boring and id prefer to be with kayla (his sis) to be completely honest... is this bad... should i stay with jack or go with his sister...