I don't understand about the alpha Omega thing going on between the new guy with shoulder ...

i think its cause the new guy is an unmarked omega and so his pheromones reached the ML alpha. so he had to take a little cold shower to wash it off(?) or like cool himself from the omega pheromones. and yeah the society in this manga still shows a bit of stigma towards omegas, so the new guy was trying to be careful of alphas

The biggest thing in ABO universe is pheromones. It's something real, btw, but it's especially exaggerated in ABO, where omegas use pheromones to attract potential alpha partners, and alphas use pheromones to push other rival alphas away. After bonding between alpha and omega, the omega's neck is marked, right on top of that pheromone gland, to stop the omega from affecting other alphas and forever bonded to just one alpha. But alphas can have more than one omega partners, so to speak. It's all ABO biology.

MC here is bonded to ML, so he's not affecting anyone other than ML. But the new guy is not bonded because he, an omega, married another omega. They cannot bond like alpha/omega pairing. Also, the new guy has excess pheromone disorder, which mean that he's affecting nearby alphas even more than usual. Considering the new guy's reaction, he was probably attacked a lot by alphas in the past.

When ML met the new guy who is close to his own heat cycle, the excessive pheromones affected him, which leads to him dousing himself in water to get rid of it. That's why he hates it, because even though he's already bonded to MC, he's still affected by other omega's pheromones, and that's just how ABO biology is.

So is his reaction not because he's an omega with the pheromones (bc it would be really weird to react like that just because he's an omega. I'm sure alpha and Omega are integrated into the society) but because he's near his heat and it affected the ML? Alright I can understand this. Haha