Angel's novel was announced by Zig but has not yet been written. What we know about him appears primarily in *Kiss Me Liar*—where Keith shares a bit about his Omega father—and in *Lick Me If You Can* (the novel about Grayson's parents), where Koi meets Angel. The other novels contain only the occasional passing mention of him.
Oh... I forgot to mention that dominant omegas have long lifespans and retain a youthful appearance, even in old age. That’s why Koi (Grayson’s father) looks like a young man, even though he’s around 60. Hahaha. Dominant omegas are amazing. That’s why there’s such an intense desire for them... which partly explains the title of this story ("Desire Me If You Can")—the other part has to do with Dane’s own guarded nature when it comes to love.

I realized that many readers didn't understand the fit of rage that drove Dane to smash a bottle over Grayson's head.
To explain in detail: in Zig's universe, a dominant omega is usually the strongest being, capable of knocking alphas unconscious with their pheromones, masking their secondary gender—even during tests—and hiding their uterus; they also possess healing abilities and a high probability of bearing an alpha child. They are extremely rare and can only be forced into heat if five alphas act in unison. Consequently, they are viewed simultaneously as a threat to alpha dominance and as an object of desire.
Since Dane is a rare dominant omega—and in this universe, they are hunted, kidnapped, and sold to wealthy families to serve as "baby factories," much like what happened to Angel (Keith's father)—his primary concern is his own safety. He doesn't trust Grayson and fears what might happen to him if the truth about his nature were to leak.
Furthermore, Dane loathes Grayson because their initial encounter was disastrous. He hadn't realized Grayson was on the verge of being raped at that pheromone party; arriving late, he only saw Grayson driving the twins into a frenzy and assumed he was acting out of sadism, rather than reacting to the violence the twins were trying to inflict upon him. To make matters worse, subsequent interactions did nothing to improve his opinion. He views Grayson as a dangerous, meddlesome, and unstable alpha.
At this point in the story, Dane feels cornered by Grayson. In Dane's mind, this poses a serious threat to his safety, as he is unsure of Grayson's true intentions—wondering if he is just another deranged alpha who might kidnap, imprison, and enslave him, or sell him off.