As a child of an alcoholic, it's hard to sit here and think "Good, do people think we're all horrible monsters? Are we lumped in the feral child category?" I can say with certainty that my AM's ex (may he rest in peace) was the only relatively healthy person in my life at a time when I needed it most. Yes, he eventually left her, but it was her drinking that did it, not me. I loved him. talked to me and did things with me that I enjoyed. He always encouraged me to do my best and overcome my circumstances. I only wish I had longer with him before he died of heart failure.
Instead of thinking about how awful this kid probably will be and stressing about his mother (who is NOT your partner), why not consider all the good you could bring to him? You could be just what he needs to heal and recover.