Should I go (long story just so you know)?

His death wasn't your fault. Sure you could have told him not to fight or told on him when he was taking drugs, but in the end everyone is responsible for their own actions. You can't control other people no matter what you do or how hard you try. If it will make you feel better, you should go, but not by sneaking out. Tell your parents everything. Sure they are going to get mad, but you are trying to deal with the loss of your friend, so I'm sure they will not be so hard on you. Tell them you need the closure and you need to visit his grave to get over it. They will probably let you go and probably take you there themselves since it is that important to you.