She used to have four children, but one of them is lost.
Not in a wandered-away-while-Mommy-was-shopping-for-purses-in-the-department-store sort of lost, but more in the metaphorical sense.
He thinks he’s done wrong by his family, so have sequestered himself from them, avoiding contact; not returning phone calls, emails, or other attempts to reach him.
His family is distraught and heartbroken over this. They miss their son and brother and want to know he’s safe, but more importantly, that’s he’s loved, despite what he has done. This is unconditional love, but he doesn’t seem to understand this concept.
They hope that soon he will make the effort to reach out to them, but know not to hold their breaths for this. So until he makes the step, he will continue being lost to them.