My adopted son asked why his first mother left

Dear Delyara, My son is eight. Tonight, he asked why his first mother did not keep him. We have always spoken honestly about adoption in age-appropriate ways, but no book prepared me for his face when he asked, “Was I too difficult?” I told him no. I said adults sometimes face circumstances children cannot fix. I told him he was loved before he knew us. He listened, then asked whether I would ever leave too. I promised I would not. The words came quickly, but my body filled with old fear. My own mother left when I was six. She packed while I was at school and never returned. I became an adoptive parent partly because I believed I understood abandonment. Tonight, I realized I still carry it like an unopened letter. After my son fell asleep, I stood outside his room checking the door again and again. I want to give him security. Instead, I am terrified that my fear of leaving will make me hold him so tightly he can feel the panic underneath the love.