Anyone with a heart, with a family, has experienced loss. No one escapes unscathed. Every story of separation is different, but I think we all understand that basic, wrenching emotion that comes from saying goodbye, not knowing if we'll see that person again - or perhaps knowing that we won't.
[Those aren't his words. Nico hadn't known her well, but he had known her. All he means to say is he's sorry.]