Hi C.! I will tell you my story, if it helps you, then I am happy that it does. I just want to inform you as best I can so you can make a good, informed decision for yourself.
I was with my ex for almost 10 years. We were married for the last two years of that relationship. When we first started seeing each other, I had asked about his finances. He said that he had made some poor choices in the past but that he had a good handle on them and was resolving them on his own. We kept all of our finances separate, he gave me money each month to pay for his share of bills and household expenses. The money never went far enough as he kept a large portion aside for his debts. We decided we wanted to have a child together and so got married and had our incredible daughter. I discovered one day, as I was going through a file cabinet of his looking for an address for him, a file that was titled "Bills to be Paid." I was thinking to myself, "What is this?" Now I am a VERY trusting person and believed in my ex that he had everything under control. I married him believing this. I looked through it and discovered debt that totaled over $100,000, owed to the IRS, past due child support for his second child, college loans, etc. Freaked me out to say the least. I am a very strict money manager. My credit score is excellent. His, come to find out, is lower than low as you can imagine. I divorced him because of this problem.
During our entire relationship, I got tired of never having money to do anything. We could never take a nice vacation, I could never shop for clothes, could not afford to buy a home, couldn't afford some months to get a haircut! I am not talking extravagant vacations or designer clothes here! I got so tired of working equally as hard or harder than he did, bringing home a good paycheck, and watching it all being put toward bills that I had no part in creating. I just got so tired of it all, no matter how much I loved him. I loved him so very much but after a while, I just got so worn down from it all. Luckily, I had purchased my home before we were married (he couldn't apply for a home loan with me as his credit score was bad, and I had received a large gift from a family member as a down payment), all of our finances were kept separate, etc. When we divorced, I walked away with everything, as I had kept it all separate. This is key!!
I STRONGLY advice you and your fiancee to seek credit counseling. There are organizations that are free, non profit organizations that will help him tremendously. Money is one of those subjects that are so hard to handle along with emotions. You have to separate your heart feelings for him and your brain thought on money matters. You have to treat money like a business. I follow that motto, "It's nothing personal, it's just business." It may seem cold, but there are very few things in life that are so completely impossible to overcome than mountains of debt. It is something that will nag at you and nibble away at your relationship. Hurt feelings happen. Resentment happens.
So, it is a question you have to pose to yourself. Do you want to live this way for the rest of your life? Only you can make that decision, but make the decision based on information. Inform yourself, seek counselors through church, organizations, etc. Gather as much information as you can, then decide. Whatever you decide will be the right decision for you.
Sorry for the long explanation. I believe knowledge is power.
Good luck!!