These people are engaged and paying for fertility treatment for five (5!) years and they haven't bothered to get married? What is wrong with them?
Could be she wouldn't marry the guy unless proven he could give her children - some gals with their clock ticking get a little unbalanced. 5 years is a really long time.
I'm no professional, or even a sociologist, but I would wager that this couple will either A) never get married, or B) marry and eventually divorce within five years.