
From what I understood, previously in highschool Ayame first took an interest in Shuu because of the ruckus around omegas however this constant teasing and joking ended up with him growing fond of Shuu. He grew protective of this omega and believed that he could protect him due to his inability to notice omega pheromones.
Shuu, on the other hand, found Ayame bothersome and scary at first but for someone who is a loner, through these frequent interactions he came to enjoy Ayame's presence. I think these may have been the starting point for both of their feelings.
Ofc, Ayame and Shuu must've been happy to have been reunited later on but the way Ayame is, its hard to tell.
In Ch. 6, Ayame doesn't bite Shuu (instead bites his hand) because of his belief that omegas should be seen as person and that two people can spend the rest of their lives together through their own choice, rather than such a thing called bond.
You could argue that establishing a bond would provide Shuu more protection but I think we can respect Ayame's decision to let Shuu have freedom. Because before being an omega or an alpha's partner, he is first and foremost a PERSON.
ohohoho, who is this new handsome fellow we are being introduced to~
a killer...
a handsome killer*