Whoa, let the facepunches fly!!!
In all seriousness to the OP, if you are going to get married, then these are your student loans that are overdue, your car payment, your phone bill, your credit card bills. If you are not prepared to take on these debts, then you really need to reconsider getting married. It sounds like there is a little one in the picture, so let's just assume you're all in. And to that, I say Good for you! You're a good man, Charlie Brown.
Now, what do you do? I think that is pretty well covered up above. Cut back on everything. Cut to the bone. Sell your fiance's car. Cut your phone bills to the simplest possible. Establish an emergency fund. Pay off those student loans and get out of the garnishment. Eliminate your (yes, by your I mean your fiance as well) debt and get both of yourselves in the black. Do this together, and it will make your marriage stronger. Avoid it, and it will be a cancer that follows you for years, and may fester into a growth that drives you apart. Do it together, or get out now.