The question is did they want to get married anyway? If I wanted to marry a guy, than I'd do it. §He would be my man, a year, two or three from now. Our wedding would be about love not about going away.
The feeling of unknown ahead of you tends to intensify things, if you're not sure. It's the need of keeping things as you know, of familiarity, of... not change. Of at least one certain thing in your life.
So it all revolves towards their feelings. What I'm trying to say is that he can be doing the right thing for the wrong reason or the right thing for the right reason. As a mother, you have every reason to worry

. Just be there for him and be honest to him. No other kid can ask more from a mother!