Leave?

my boyfriend is an addict. 4 in one special Weed cigarettes alcohol and  meth Not trying to make a joke about it this is very serious he’s been doing it  since he was in high school he is now 32 years old I have known him for about eight years just as friends we recently started dating and he continued to use I have been around many attics but never involved with one. My mother father aunts uncles have all had addiction issues I myself have never smoked a cigarette in my life I’ve always had self-control and taking care of others so when it comes to addiction.  I have no idea about it he was clean for several Weeks.  Even months He was going to work every single day coming home happy I never see him smile so much we went out on Thanksgiving to the casino with a few family members and that night he did dope again and hurt me so bad and I’m not really sure what to do I don’t want to leave him I don’t think it’s right to leave him alone because I can only imagine what he’s going through but is this fair for me? Would it be wrong for me to leave him? Is he truly sorry?  How my supposed to trust him again knowing any moment you could relapse ?