If a person is behind on life milestones or doesn't quite have their shit together on the surface, what matters more than their situation is how they about it.
Are they just unmotivated as hell (in which case, NEXT), or are they only behind because of a big sacrifice or setback in their life?
Some people simply don't like splashing their personal life onto social media or even talking much about their feelings with friends, but that's different from flat-out hiding your partnership, which is about as glaringly red as a flag can get!
We are all insecure on some level, and it's nobody's fault for feeling that way, but no reassurance from a partner will ever be enough, because those issues live inside the person feeling them.
If insecurity dictates a person's life, it can just as easily dictate their relationship.