How to live after losing your only son?

I just lost my son 23 years old, three months ago and it feels like yesterday. My only son, my only purpose in life. The best part of my life, the only good thing in my life. I don't know where to go from here. I lost both of my parents three yrs ago. My sister is with the man responsible for my his death, her husband. A narcissist selfish prick that took him to an illegal racing knowing my son was deaf and the danger he could put him thru. He was the one driving and racing another cars with my son as a passenger.... there's more but I can't talk about it yet. My son was the best kid l've ever known. He was kind, loving, sweet, always thinking of others first.... My life has no purpose and l'm trying desperately to find one.