Spoiler

Chase didn't do it with a dog. Grayson lied and wanted to scare Chase. Grayson manifested as a Dominant Alpha very young and so his brain got fried from pheromones accumulating. All dominant alphas are fucked up in way or another bc of the excessive pheromones. In Grayson's case, he has a hard time understanding emotions. However, he does love Chase. But his way of understanding love is fucked up. In his mind, since Chase refuses to have sex to release his pheromones, Chase will eventually die from pheromone accumulation. So the only way to 'convince" Chase to find a partner and safely release his pheromones is to scare him into thinking he blacked out and had sex with a dog. And it worked to some extent bc after lying that Chase had sex with a dog, whenever Grayson went to find Chase,.Chase would obediently go with him to an orgy party. Granted, Chase would still refuse to find a bed partner and instead take drugs to release his pheromones, it was a better alternative than before. It is also for this reason -making sure a Chase didn't accumulate too much pheromones - that Grayson would go find Chase every few months.

Grayson explains all this to Joshua later in the novel. And Joshua justifiably punch Grayson for his psycho reasoning in traumatizing Chase.

Also fun spoiler, Joshua teams up with Dane to kidnap Grayson. Joshua wanted to have Grayson kidnapped and give him to Chase as a gift. He wanted to let Chase vent out his anger and beat Grayson to a pulp. It was gonna be his birthday present to Chase lol.