User blog comment:The Dragon Demands/The History of House Targaryen. Part IV: The Dance of the Dragons/@comment-5014364-20131115095205

The problem was that the Targaryens kept cheating on each other, because they had only political marriages. The rumor was that Rhaenyra had Harwin Strong *and* Criston Cole as lovers at one time or another, leading many to suspect that her three sons by her first husband (Laenor Velaryon) were actually Harwin's sons. Laenor had died, so Rhaenyra remarried to her own uncle Daemon, and had to sons with him. Criston Cole was so angry that Rhaenyra spurned him (possibly for Harwin Strong?) that he became a staunch supporter of the Greens and indeed crowned Aegon II.

At any rate....Daemon wasn't exactly faithful to Rhaenyra either. He'd already had a first wife - Laenor's own sister Laena Velaryon, and had two children by her (Rhaena and Baela). But apparently...Daemon started having an affair with Nettles. Rhaenyra got so upset about it that she sent orders to the castle they were staying at to kill Nettles and/or Daemon. The garrison was shocked, as Rhaenyra's orders explicitly commanded that they violate guest right by killing Nettles while she was still formally a guest under their roof.

POSSIBLY the death of Nettles is what made Daemon decide to hunt down Aemond, damn the consequences.