Boris Ivanovich Krilov is Nina's husband. His last name is likely the same one she uses (Krilov) as she never obtained a divorce. During the first part of their marriage, they lived in Vladivostok. At some point, Nina aborted their child.
Boris loved Nina and begged her not to leave him to join the KGB. Once posted in America, she regularly sent him money and other items she obtained illegally. Boris eventually lived with a woman who bore him two sons and was happy they sat "at the same table, ate the same food, shared the same bed."
In March 1983, Boris meets with Nina at the Soviet research facility at her request, and agrees to deliver a message regarding Anton's son. The note is ultimately intercepted, resulting in Nina's death and possibly causing Boris legal complications as well.
Boris opined that his "world was too small" for Nina.