I wonder if someone could explain the nature of this feeling of Riker's.
Both Rikers (or is that both Trois?) had some traumatic times between "Insurrection" and "Nemesis", some of which was related to their families. If you only want to get a glimmer of Will Riker anguish, the duology "A Time to Love/Hate", within the "A Time..." series, would be an excellent place to check. There was also the trauma of "The Battle of Betazed", "Nemesis", and the death of Data.