Hi Mayer,
You've ended up in the right forum and I wanted to welcome you. I can only imagine how overwhelmed, scared, upset, etc. that you are feeling right now.
My guess is that your financee has a pretty major problem but if he is like a lot of users he will minimize it. The thing about it is that you so badly want this to be different and don't yet know enough about drug use/addiction that you will possibly believe what he is telling you.
This is big deal stuff - trust, drugs, betrayal, fears, doubts, and financial issues. And all right before you are supposed to marry. On one hand I believe that you are extremely fortunate that you found all of this out before you married him. I hope that you will at least delay your wedding until he has been sober and worked a recovery program for at least a year.
Recovery from substance abuse is generally a long, slow, and difficult process. It is so much more complicated than most people realize. Once a persons brain has flipped the switch to addiction then it is permanently flipped. It sounds like your fiance might be addicted (financial issues, lying, staying up late, friends that use, etc) so I would be extremely cautious regarding taking your relationship to the next level. I'm not saying not to marry him - just give it time until you know what he is going to do and if recovery is truly something that he is going to work out.
Years ago, an addiction counselor told my husband and myself that the only way that a relationship with a recovering addict can work is if both people work a strong recovery program. I have had to work the same recovery program that I wished that my husband had worked.....my own program has helped me to endure the last 6 years. I know what it is like to live with someone in active addiction, early recovery, and then sobriety without a recovery program. It is tough going and definitely something that you want to think long and hard about.
I know that you love him and want things to work out. I can also guess that you want to stand by him and support him. You can do all of that without legally being bound to him though.
There are so many things that you can do to help yourself....and honestly, that is the best way to help him. You can start by reading all of the sticky's at the top of this forum, read Co-dependent No More by Melody Beattie, go to at least 6 face to face Alanon or Naranon meetings. I would also try and find a counselor that is able to give you individual support.
Please keep posting here - there are a number of other people that have found themselves in similar situations just before or after marrying. You are not alone. I'm sure that other people will be along to welcome you and introduce themselves fo you.