Struggling to get trust

well this is the first for me.. I know i need advice on how to handle my problems. me and my boyfriend has been dating 3 and half years now. December holidays that past he started to use a drug called Khat I'm totally against drugs and he knew it from the start. He was hiding it from me till February when him and a friend got pulled over by the cops and almost went to jail. but then he couldn't hide the truth anymore. well after then our relationship trust went out the door, i cant TRUST him anymore. well then in March i got some more in his jacket pocket a full bag half bag and a empty with his straw. I went nuts i even took him to the police station in the state i was in i tested him and it showed a positive. He started crying and telling me its not his he promise me that ect. he told me someone set him up i believed him as i know his friend is mad i didnt leave him so that he can do what ever he want. coz if i had to leave him what wouldve happend to him. Then now in the week I went to have drink with his friend yip that one. i wish i didnt as he told me about how many things he lied and when i confronted him he said somethings weren't true and some were. how do i take it from here i love him to bits. and i cant see a life without him how do i get over the past??? how can i forgive him for hurting me so much. is his friend just hoping for me to leave him so he can just carry on with his old ways?

if he loves you enough he will get help and stop!! only then can you trust him again. but he needs professional help and probably wont be able to do it alone. he will also need support from his friends and family and you if you choose to stick around.