Hi Tammie and welcome,
I am so sorry you are going through this horrible and tragic time. Your fiance was so young and his whole life and yours was laying before him just waiting to be lived and enjoyed.
I know I keep looking for answers too because my son, Jeremy who was 35 overdosed on Thanksgiving sometime after midnight and was found by a friend where he was staying. I know he was depressed off and on throughout his young life and had a drug problem but he seemed so happy and was staying clean and planning his future. He told me one time that someone usually commits suicide when their lives are happy and does not tell anyone when they decide to do it. There are no answers is what I have come to and the realization is they just wanted the pain of depression to stop which is a horrible curse.
Please take care of yourself and just know this was your fiance's decision and you loved him and have good memories of your time together. A good book on grief is an excellent way to help you through this time and see a counselor. Stay busy, eat well, and get plenty of sleep to help you traverse this difficult road. Remember the good times together and celebrate your fiance's life.
Charlotte