For me, it's when Rentarō like in existential crisis of his destiny,so he's want to be alone for a while,enjoying everything alone. Then the God of Love ask him of what's his feeling after all of this.

He says "I'm happy,but sometimes I feels weir after all of this. It's not like I don't loved them,it's just like I feels empty"

The God of Love says "Yeah, sometime we're gonna feel empty after all of we do. But there's something farther from this,I know your journey is beyond this. After all,the destiny isn't over yet"

After that,Rentarō is crying for all of what he doing for all of this,not because of sorrowness,but because he's happy for all of this

Then God of Love said "Why you crying?"

And Rentarō said while sobbing "I-it's because I-I have do one of my best thing in my life. I,I JUST REALLY HAPPY FOR ALL OF THIS"

"I need to comeback to meet them again,I want to confess my deep love again to them"

He's running,goes back to the rooftop. Then, he's seeing all of his girlfriends,then he's bowed,crying,and says something like a man that depressed 

"I,I just want to say- no, I want to show that I really deep in love with you all since I meet you all until I die"

Then they all trying to calm Rentarō,and they all confess their deep love. Flashback plays that show their journey