
So, yashiro can't remember seme (sorry i forgot his name) for 4 years?????? I'm crying

Yashiro pretends he did not remember Doumeki so the latter will go back being a civilian.
Doumeki was not a Yakuza officially so he has still the choice to opt out, while Yashiro is a full pledge and knows that even he somehow walk out as a Yakuza, he will still be tangled with the Yakuza world.
I think he does not know that Doumeki continues being Yakuza and became a member.

Indeed, I think rather than visibly being pleased after a collision, Yashiro will be faced with complex emotions, such as whilst feeling somewhere inside him pleased, mostly shocked and saddened that Doumeki has not returned to civilian life, and once again Yashiro feeling guilt over this. He saw Doumeki nearly die for him, and due to this cut him off, along with his trauma of running away from the fear of someone loving him, and showing Doumeki himself at one of his weakest points. Yashiro has not had to really confront any of this, in the past 4 years, he's busied himself with work, and also felt undeserving to get his eye treated, instead wishing he was made fully blind. The author has certainly given a lot to be worked on!
Finally they do it after just the 'tip'