There are many different questions you need to discuss with an Immigration attorney: did he come through the border as a "waive in" alien, or did he come without any inspection? He stayed here for 10 years: criminal convictions? Will he be willing to enter the removal process voluntarily to get (if he qualifies and is willing to take the risk) cancelation of removal?
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It would be best to have an in person or over telephone conusltation with an immigration lawyer on a one on one basis focusing your fiance's situation. Your fiance's entire immigration history needs to be assesed keeping in view his current status and the law. Best Wishes.