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Am I your shared boyfriend? Is this the polyamory everyone talks about?!

"Please go out with me!!"
Hajime confessed to Uno, a junior at his part-time job.
She accepted his confession, which he hadn't expected to happen...
But his excitement is short-lived, as he is confessed to by An, a senior at his part-time job...
He honestly told her that he had a girlfriend, but she asked, “Then why don't the three of us go out together?" What does that mean?!
Uno agrees, and a strange romantic relationship begins...].

Then one day, he was alone with An-senpai.
"I'm also Uno-chan's official girlfriend!"
An-senpai's aggressiveness made my penis about to explode!
I asked, "Can I put it in? Is it okay?" but was it wrong??
I'm sorry Uno-chan!! I can't take it anymore!