Would you stay with a guy/girl you've been with for 9 months (and has been telling you they love you) if they told you once their child leaves home they don't know how they are going to feel about you because their life will be so different? A week later I told him the comment was really bothering me and I said maybe we should take a break or break up until his son does leave. I had to go on a week-long trip the next day. When I came back he told me he'd had a change of heart and knew for sure he wants me with him after that time and that I need to forgive him/get past the comment if we're to move forward. A week later on a trip away he said he had to ask me something and asked if I wanted to move in together after his life clears. He hasn't mentioned it since though.
I think the comment was pretty insensative on his part, but if heis actions match his words at the moment regarding his change of heart, I'd stay.