?

I gonna drop a message so I can know too

Im pretty sure its because he thinks he raped an omega (that time he got into heat and did it with Josh). And so now he rather avoid them or something like that.

Not exactly an omega he thinks or rather believes that he raped a dog when he went into rut for the first time although he didn't it's just his elder siblings specially that blonde actor guy( from kiss me liar;damn I keep forgetting his name) made him believe(PS they did it for fun pisses me off everytime i remember how traumatized chase was)

I don't think the blonde guy from kiss me liar did it. I think it's his brother that told him he raped a dog

Yeah and the blondie alpha from kiss me liar is his brother duh

i think the brother's name is greyson

Yeah yeah Grayson now I remember thanks a lot

Omegas can manipulate alphas with their pheromones. You saw what happened to Chase in chapter 14?
Chase doesn't want a relationship based on instincts, manipulated by pheromones.
In addition Chase tends to pass out during ruts or can't remember what happened.
He hates to lose controle and is afraid he hurts someone.
Chase is pretty sensitive for an dominant alpha, because he presented very late.
Which made living with his early manifested siblings extra hard. And he fell victim to Grayson's weird way of helping attempt which caused a trauma.
And, well, the Millers are all crazy one way or another. If you think Chase is the only one who decided to get injections instead of spending the rut with someone they don't love, your wrong. The moment a Miller truely falls in love, that's it.