Why did it take so long for Clark to realize what a monster Homelander was? Clark was just as desperate as Homelander to have someone he could relate to. Despite all of the genuine relationships Clark has cultivated, knowing he's the last Kryptonian makes him feel an almost crushing sense of cosmic loneliness. So, it's natural he would look to Homelander as not just a role model but also the only being in the universe similar enough to one of his people. On a subconscious level, Clark just... didn't see who Homelander really was.
