Step Children

I need to get this off my chest as I have no one else to go to. my husband and I have been together 11 years and he has a 12 year old son, we have an 8 year old daughter together. My issue is it feels like he always puts him first over our daughter. I have felt like this for a while but something that has happened recently has brought it to the surface. Our daughter hasn't been a well child from around 1, she has issues with her kidneys and get infections easily, recently she was rushed to hospital with suspected sepsis, he didn't bat an eye lid and stayed at work while I was in bits and she lay there weak and drained. This weekend his son has hurt his knee at football and needs to have his leg plastered. He has booked the day off and shot up to the hospital to be with him!! Why? I am so confused. don't get me wrong I love my step son and know he will be in pain but it's not life or death. Am I being selfish??