"The things that are running through my mind right now : am I doing the right thing? What do I tell my friends? my family? what do I do with the honeymoon tickets?
The right thing - yes. To save both of yourselves. Only you know the right thing, because it is your life. No one else can fully tell you what is right or wrong for you - but I will say that with your knowledge and experience that you know you are doing the right thing - unfortunately you are just so beat down in co-dependence and you are having trouble trusting yourself. Trust yourself... you know all that you have experienced. Stay true to yourself.
You tell your friends/family that it turns out your fiance' has a very big problem - in fact - you are really glad that you are catching this before you become an ex-wife or even a widow. You let them know that you have turned over every stone and that there is nothing you can do to stop him from hurting himself - and in the meantime - you aren't going to play any role in it - you have done your homework and the best thing for you both - is to "let him fall" and to let go.
Honeymoon tickets....... do you have a best friend you can take?
I really cant believe that he is back to where he started 2,5 years ago.... And the sad part is that he's denying all of it. But i guess that's what drug addicts do
Yeah... that is what addicts do. It made me sick with my *x* would deny it. I think about just how much denial he is in. There were times I wanted to video tape his denying of being high or even coming down - and then have it to show him one day just how convincing he was himself - yet so unconvincing to myself and others. It is SO sad. 
I gave him a last chance 4 month ago, when he got drunk and the next day he woke up with marks... He did confront us (his mother and me) and i agreed to trust him for a last time....
I want to give him another chance but i understand that it wont lead anywhere....."
You can always get married ........ later. Before you give him a second chance..... think to yourself why you are allowing this or even wanting this... is it worth it? Is your love worth it? What is it that is keeping you?
Then.... when did it become okay for him to lie straight to your face? And that you end up second guessing yourself because of HIS lies?
Right now you might be running on adrenalin ..... so be careful about what you say or do...... because you want your actions to match your words. What you say and do ..... to line up. Don't allow his disease to over-run you.... get yourself centered... and think about yourself..... cause he isn't.
He has a disease.... and one that can and will hurt you just as much as it does him. I love the person and I absolutely loathe disease of addiction. I will not ever allow it to rob me of my life again.
Welcome to SR, btw. I'm sorry it's under these circumstances.