Listen dear heart,
I hardly know anyone who wouldn't feel guilty after loosing their lived one, myself included. It's not easy to loose loved ones, it always a tragedy.
My kids have 7 years difference in age and also not very close growing up, only when my daughter got married and left home, my son grew up too so they got closer. This is always a case, don't blame yourself for this.
Especially in between bro and sis.
I am sure he knew you loved him and he loved you back. Just so tragic that he had to die at such young age. I am so sorry to hear this, this is so unfair... I wish I could help you to ease your pain, but I cant.
He wants you to enjoy your life, your marriage and your new house... Let the guilt go, it will not help you to build healthy happy life and this is what exactly your darling brother wants for you.
Stay strong, hang on in there