I am really sorry that you are going through such a hard time. The emotions you are experiencing are completely normal and your friends should try and make allowances for your situation and be there to support you. In my opinion your friends should be more sensitive and not say that you are using your step dads illness as an ‘excuse’.
Maybe your friends just don’t know how to help you best, but I am sure they do care. My friends acted in a similar way when I was going through a hard time, they simply didn’t know what to do or say so consequently they did nothing. Maybe you should take aside your closest friend and explain it all and just say you need someone to talk to.