I stopped and now they notice

I've been cutting for about a year and a half, but I stopped a little over a month ago. After I stopped, people started pulling me over in the halls(I'm in high school) to ask. The ones that hurt the most were one of my best friends, and my own father. When I went to get help, I went to my mom. I figured she had told him everything, because I hadn't. She didn't, and he grabbed my arm the other day and started asking over and over where they came from. I wanted to cry. I ended up saying they were old, brushing him off and walking away. When he asked again, I told him that everyone else already knew, which was relatively true. He lives with me. I had been cutting for over a year. He had seen one sit on my sister's arm and locked away every dangerous object in the house for six months(except my tools because he didn't know about those). I had already thrown them away when he asked, but I spent the whole night searching for replacements. I didn't find any. My best friend noticed less than a week ago. It's weird to me because he asked, and I thought of all the times I saw him the day after I cut or how I couldn't pick up our thirty pound robot because my whole arm was cut and would start bleeding. Or the time I got a third degree burn from a glue gun and I brushed it off as having dropped it. Only one person noticed while I was still cutting. The girl I sit next to on the bus. It makes me wonder, how many people saw, but chose not to? How did the people I love see and look away?