The reason why yuri decided to ‘end this’
The scene when Yuri can’t find Victor and finds him watching Yurio’s scores, he realizes something.
He realizes he is holding Victor back by making him his coach until he retires. Yurio has beaten Victor’s world record, and he realizes he’s the ball and chain holding him back to only watch from the sidelines as other skaters beat his 5 year reign.
He sees him being inspired by Chris, and his longing to get back onto the ice to take back his throne and compete with them.
Yuri watches as skater after skater after skater beat him in the short program , and Yurio (whom he had beaten on onsen on ice) get the winning position and mock him relentlessly.
And when Victor looked inspired and said ‘He’s great, that was very exotic! It felt so fresh!’ He flinches again, as Victor praises other skaters.
He knows he has let Victor down, himself down, and everyone he had promised gold to.
His insecurities flare up again, as he realizes he is not good enough to win the Grand Prix Final, and that he’s pulling down Victor with him.
Instead of Victor making that choice to abandon him (in his mind) he decides to do it himself.