Wolverine knew for months that Jean Grey has returned after they believed her dead, but he didn't tell his teammates. He had caught her scent several times: in the Morlock tunnels and at her parents' house. (Uncanny X-Men #212, #215))
When Illyana Rasputin (Magik) died of the legacy virus, the X-Men buried her on the Xavier Estate and her funeral was interrupted by Magneto attacking the X-Men. (Uncanny X-Men #303-#304)
Young lovers while attending Oxford, Charles Xavier and Moira MacTaggert were to be married, but he was drafted and sent to Asia. While there, he received a letter from Moira who dumped him without explanation. (Uncanny X-Men #117)
Dazzler was pregnant with Longshot's child. It's been speculated the child will grow up to become the former X-Force member Shatterstar. Dazzler's pregnancy has not been mentioned since in the comics; the child may have been born and never seen by the readers, although evidence suggests that Dazzler may have had a miscarriage, though it has not been established officially what became of the infant. (X-Men #11)