I feel terrible

I just had twins two months ago and I've been really stressed and a little sleep deprived. My husband isn't much help with the twins. My 14 year old helps sometimes but he's at school a lot. I feel terrible because today is my son's dad's death anniversary. He's been gone for 5 years. Every year me and son makes his dad's favorite cupcakes and listen to his dad's old CDs. His dad was really into heavy metal. My son told me today "You forgot dad's death anniversary." I said I was so sorry. That I've been really tired from the twins. He said it was okay but he had tears pouring down his face so I know it's not. He told me he's been gone a long time and it shouldn't bother him anymore and I have new kids to worry about. Of course that's not how it is and I tried to tell him that but he kept saying it's okay and went into his room and listened to his dads CDs by himself. I feel so bad. I've just been so tired.....