My daughter and my sister boyfriend

My sister has been taking care of my daughter for the past 5 years I was on drugs and my sis was there when I was at the lowest point of my life I had lost everything I had she took my kids and helped me I love her so much for that I been clean for the past 2 years I had a baby and got my son back for a year now I got a job a car work so hard for my life for my kids for my self my daughter did not want to move in with me she wanted to stay with my sis she is 17 will be 18 in dec about a few months a go she was at my house and the hole time she was there I say my sis boyfriend name pop up on her phone I was like why u texting him she did I ask him a question I had this bad feeling and I was like what is going on I told my sis how I feel and they both was mad at me for saying that they was talking and I was looking in to it the wrong way I was like she is 17 and she been here two hours and here phone going off every min and I see his name so we left it alone I just asked my sis please open yours eyes then come to find out after a few months my sis open her eyes and saw what I saw she asked them what is going on they said they only kissed and held hands but we all as a family think its so Mucho more she was all about him this man is 23 years old he know better my sis just had a baby in Jan they been going through two much she had a few miscarriage but he had no right to turn to my daughter at all we try to call the cops they say 16 is the age for consent I am so mad at her and him I feel for my sis I am mad at my self what if I made her live with me and not let her stay with my sis this is so much to deal with