NTA, and that is absolutely horrifying. One of my closest friends had a similar revelation after she was already married, and the fallout nearly destroyed both her and her husband. In her husband's case, it was his father who had taken out the loans and racked up the debt in his son's name during the time that they were both in grad school. I couldn't even begin to comprehend how awful it must have been, it all happened or came to light just as she was about to finish her DMA and they were thinking about children. They discovered the magnitude of the debt, his mother became hysterical and refused to acknowledge what her husband had done, it was a tremendous and tremendously painful mess.

I wouldn't wish it on anyone, but I'm glad you've discovered this early at least. You are not the asshole, regardless of how you choose to proceed. I literally cannot imagine a parent finding any way to justify including their child in these types of debts. Its repulsive, and the two of you will figure out how to handle it, but I would