Should i tell her?

I have a huge dilemma, my sister’s husband has been hitting on me for the past year. They have a one and ahalf-year-old daughter. I have told him to stop but he continues to do so. I don’t know if I should tell her what’s been happening. Because I would ruin her life, but I would definitely want someone to tell me! She’s my sister and I love her a lot, help I need advice!!!!! 😓