Do not Disturb.
As someone in a long term (7 years) relationship, with no intention of getting married, not getting married does not mean the relationship is rocky.
It may mean that one or both people in the relationship have seen some nasty marriages, or seen good relationships go down the tubes right after a wedding.
It may just mean that they have the opinion that if it ain't broke, they shouldn't try to fix it.
Heck, it may even mean that they simply don't feel like the government and/or religious authorities have any business in their love-lives.
You may be able to get away with a SUBTLE reference to how lucky her boyfriend is, but leave it at that, and whatever you do, don't say anything like that often, or you will turn into someone she's not comfortable being around.