It's all within his calculations that shoukichi would come. As riku told fuku before he left, that nothing has change, despite all that happened, fuku is still the manipulative stalker he was and all of the crying and begging for forgiveness was all an act to guilt trip shoukichi. And knowing shou-kun's personality, he would feel responsible for fuku's misery without him. Hence, when they meet again, him saying back to square one means that the manipulation game will begin again until he completely monopolize shoukichi.
OHHH THANK YOU SO MUCHHH
No problem
I DONT UNDERSTAND THE ENDING??? WHY DID HE SAY BACK TO SQUARE ONE JUST BC SHOUKICHI WASNT INVITED AND DECIDED TO COME UNINVITED??? SOMEONE PLS EXPLAIN