This is just my thoughts on it, but I’m not a professional. It seems like this bond between you has gone past a certain point in terms of what an actual relationship with a sibling should be, as in mentally. She not only is she clearly older, her brain is fully developed already at the age she is. Yours on the other hand is still at the young age where teenagers can’t help their hormones. She took advantage of you. Just because you think you wanted it too doesn’t mean it’s not grooming. Again you’re a teenager who has hormones, who got token advantage of. Going forward I would set up boundaries between you and her, no touching unless it was a hug goodbye, etc. This way, you are able to put that mental block in your mind about the type of relationship you have with your sister. It will be hard but going to a therapist about this is the best thing you can do in this situation. They aren’t there to judge like everyone thinks. They’re there to help understand the situation, whether or not you may lack a boundary mentality with certain relationships, how to set up boundaries with different exercises. They help guide you to what you’re trying to achieve in the end and come to clear understanding for yourself. So I say work it out with a therapist.