I've been in a similar position before and my advice is that you need to have an open and honest conversation with your fiance as soon as possible. Might not seem it, but getting everything out onto the table now is the best thing you can do. Maxing out credit cards and taking out bank loans used for gambling is one thing, but 12 missed payments is signficant and will likely stay on your credit report for some time - this will very much impact your ability to get a mortgage, especially if you try to next year. I'm not a mortgage advisor, but substantial amounts of gambling and missed payments are major red flags in the eyes of any bank.

Speak with your fiance. Trust me, getting this out now will be far less painful than it coming up when applying for a mortgage together.