I think he needs to figure out what he wants and not focus as much on what society expects he should want. Why can't he be "forever" with you? "Forever" is never a guarantee and just an attempt to try to be together as long as it is good for both people.
I think he should enjoy a good thing while he has it and not worry about possibilities or other people's expectations. I think finding happiness is an internal struggle to recognize all the good things you already have.