
I don't think it's anything like that. I think his mysophobia is what drew Kurose to Shirotani in the first place. Just as a "type" or characteristic that catches a person's attention... like some people are attracted to blonde hair/blue eyes, or Asians.
(There's a certain *persistent* type that targets Asians...)

If he is, then I think they both are.
I interpret the flashbacks as explaining the motivations of each character.
Just like everyone else, Shiro and Kurose are looking for love and acceptance. What happened to them as children simply shaped what that looks like for each man.
Shiro is looking for someone to love him like his father couldn't and Kurose is looking for someone to love him the way his mother never did.
I don't think of it as substitution, so much as finding a love that fits who he is on a deeply personal and unique level.
IF it ever turns out Kurose is using Shirotani as replacement, I will not forgive him! And I will possibly drop this manga because I hate those types of storylines. Don't hurt Shirotani! Please please please don't turn out that way!