It's his responsibility to bring it up, because if he thinks about it, he can relieve Heather from the obsession, and from having to make sure that the affair isn't forgotten, and that in itself begins to restore trust.
Es su responsabilidad sacar el tema, porque si lo piensa, él puede aliviar a Heather de la obsesión, y de tener que asegurarse de que la aventura no se olvida, y que en sí mismo empieza a restaurar la confianza.