Can we stop for a second and think about how, in s1, Dick tells Wally "I didn't want my best pal questioning my objectivity", only for Wally to remind him "Dude, that's what a best pal is for..."

And then, in s3, Will confronts Dick, and says "[I'm talking about] Your need for a Wally West substitute. [...] You needed someone who knows you. [...] I get it, you needed someone to give you a reality check, to keep you honest, to tell you what no one else will tell the boss."

Because despite Dick being so secretive, everyone, and I mean everyone knows the impact that Wally had on Dick. Even after Wally's death, which might I remind you is what definitely pushed Dick over the edge (taking a break from the life, hallucinating his dead best friend after saying he was alright, neglecting the kids he rescued, letting Wally's name slip, etc), nobody forgot what Wally meant to Dick.

In the YJ comics, you can even see Dick in tears at Wally's funeral. Dick, the reliable, strong-willed, military-trained one, lets himself cry in front of everyone else. Wally was Dick's only anchor to reality. Not Bruce, not the others, not even being Robin - just Wally. He kept Dick humble, grounded, even in s2 after their argument, which would've hurt less if neither the two of them nor the others were aware on their symbiotic bond.

Wally's trust in Dick's plan wavering for that moment is enough for Dick to actually question his own choices, to make him question his own grip on reality, the control he has over the situation - just for a moment, but the crushing doubt is there.

And, I say symbiotic, but I must admit that in YJ we don't really get to see Dick being supportive of Wally, not as much as we see Wally being supportive of Dick, but it's heavily implied anyway.

The chemistry between Wally and Dick is undeniable. Some ship them, some don't - but what I think everyone can agree on is that, were Wally to ever return, chaos would ensue, and Dick's control would inevitably slip.