
He did not sleep with a Dog. It was Grayson's fault for making him believe that. During that rut where he "slept with a dog" was actually the night he selpt with Josh as far as I can remember from the novel.

++++Chase was unable to remember him and Josh's night which led to pete's birth. Grayson saw that opportunity to lie to Chase and tell him that he did with a dog, and since chase does not remember at all, he believed that and ever since then, the thought of being with or seeing dogs scares him so much.

No, it wasn't. It was Chase's first rut, there was no Josh, there was no one to spend it with, that's why Grayson paniced and brought his dog Alex. But Chase passed out and nothing happened. Chase forgot almost everything, but remembered a dog being present and he thought that it was possible that he slep with that dog, and no one told him the truth.
(Iicr Chase knows that the night with Josh, that he slept with an omega, but can't remember much more)
And Grayson later uses this uncertainess to get him to go to the pheromone parties, which is the best way to get rid of his pheromones. Because the pheromones floating around makes it easier and for emergency or if one doesn't want to have sex, often Steward or at least his staff is present to get rid of the pheromones via injection.
Chase'S father suffered braindamage because of too many accumulated pheromones. If not Grayson, he would make sure that Chase somehow get's rid of his pheromones.

THE PANEL ON CHAPTER WHERE HE SAID HIS REAL NAME AND THEN IT SHOWS WHAT COULD'VE HAPPENED IF ONLY HE HAD THE COURAGE TO ADMIT ITTTT! TO ME THAT SYMBOLISM MEANS SO MUCH! IT'S LIKE THEY'RE FINALLY FREE TO EXPRESS THEMSELVES! AND HAKYUNG SAYING "MY TURN HAS FINALLY COME" MAKES MY HEART SO HAPPY! YES BABY! YOU HAVE ENDURED A LOT AND NOW IT'S YOUR TIME TO BE HAPPY! + I WAS KINDA EXPECTING A PROPOSAL IN THE END BUT EVEN WITHOUT THAT, THE ENDING STILL FELT SO GENUINE, NOT RUSHED, JUST PERFECT (THO, I HOPE THERE'LL BE SIDE STORIES WERE IT'S JUST THEM BEING LIVEY-DOVEY, AND HOPEFULLY THEY GETS MARRIED TOO.)
It's been 84 years...