Im lowkey confused

The first time they slept together was bc Chase's pheromones got out of hand, he went crazy or something like that.

Josh saved Chase during the terrorist and coyote attack and didn't ask for anything in return. Also, Chase has been attracted to Josh since day 1. So after knowing Josh is a good guy, he has become more comfy with Josh and now they have physical relationship. Chase just has lots of trauma and has a hard time trusting people. He thinks everyone that wants him is after his status as extreme alpha and his dna (aka semen) to create more extreme alphas.

Yeah I think they're moving too fast too, like Chase just started to trust Josh completely and now they're all over each other just like that? With Josh wanting to sleep with him so badly even tho before he didn't even want to be around him and came to work for him for money ? I thought he really didn't want to sleep with him and kept his distance. We don't know what's going on in his mind, it's missing some plot

From what I understood in the novel, Chase has a su*c*dal tendency. It can be proven by the fact that he consumes more pills (if I'm not mistaken something to deal with the pheromones) compared to his brothers.
I think, that's also the reason why Grayson lied to Chase that he spend his rut with a dog because Chase doesn't go to pheromone parties to release his build-up pheromones (by the way, there father lost his emotions because of severe brain damage cause by pheromones and he's also strict with his children about pheromones so yeah~)
Anyway, as I said, he has that tendency. One part in the novel also mentioned that Chase just actually want to end it all and it was only Josh who told him he will kill him and also protect and save him as long as Josh's is alive. And yeah, Chase is attracted to Josh too hahahaha

Well yeah, Josh wanted to stay away from Chase to protect Pete, but he's extremely weak to Chase's looks. The first time they slept together was because Josh was attracted to him, and Chase is mad about Josh's beauty from day one, though he just expressed his irritation because he really doesn't trust anyone. The webtoon seems to rush a bit and misses some of the finer details about why they're attracted to each other and to what extent.