I think your pain is so multi-dimensional it’s almost impossible for anyone to fully relate to what you are/have been going through. It is not one death that you have had to grieve for, rather three. It is not just the hurt of someone passing away - but of a failed marrage.
Go and see a qualified Doctor/Therapist. Look into rehab centres. Addiction comes in many forms and emotional addiction is as unhealthy as latching onto a drug or turning to food. Through behavioural therapy you can unlearn destructive habits and the subconsious motivations behind them.
I would strongly urge you to talk to your fiance about your fears and if possible, take the physical stuff very slowly. Try and love him as a friend and as a person and by extention as a husband before you love him as a man.
I wish you all the best. Let us know how you are doing. 