My Girlfriend Cheated on Me With a Senior, so I’m Cheating on Her With His Girlfriend

My Girlfriend is Having an Affair with Senpai (Part 1)

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When I, Yuu Isshiki, saw it for myself, my hands began trembling.

…No way… there’s no way, right…?

However, the notification that popped up on the screen of my phone cruelly told me everything—their relationship.

> (Kamokura-senpai) Karen, are you home yet?

> (Karen) Yup, I just arrived.

> (Kamokura-senpai) I just got home too.
But Karen, I already miss you.

> (Karen) Me too! I can still feel Senpai’s lingering touch!

> (Kamokura-senpai) [Good!] stamp.

> (Karen) [It was the best!] stamp.

> (Kamokura-senpai) Seriously, Karen, that was so good.
Why don’t you become mine?

> (Karen) Eh~ don’t you have a girlfriend already? Sakurajima-senpai, right?

> (Kamokura-senpai) But, you know, I think our bodies are really compatible.
Don’t you think so too?

> (Karen) I do!

> (Kamokura-senpai) Right? That’s why I want to keep having sex with you.

> (Karen) We do it at least once a week already.

> (Kamokura-senpai) I want to do it every day!

> (Karen) LOL.

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> (Kamokura-senpai) By the way, Karen, didn’t you say it felt better than with Isshiki?

…

I didn’t want to read any further than that.
I couldn’t.

I won’t scroll down.

After quickly taking a picture of the messages, I noticed several similar conversations.

The dates—definitely all days I hadn’t seen her on.

Apparently, Karen was “hanging out with friends”, “going out to dinner with family”, “finishing a report tomorrow,” and so on.

Karen Mitsumoto—my girlfriend—would, on those days, meet Tetsuya Kamokura, an upperclassman in my circle.

…They went to love hotels, and other such places.

According to online relationship advice for girls, it is the boyfriend, not the girl, who was at fault.

—It’s the boyfriend’s fault for not trusting her—

—The boyfriend doesn’t care for her enough, so she cheats on him; in other words, he deserves to get cucked—

—It’s not allowed to look through someone else’s phone without permission; they’re the lowest!— 

I put Karen’s phone back into the jacket it was in.

Karen had recently changed her phone’s security.

Her fingerprint authentication hadn’t seem to be responding well, so she switched to using a PIN code.

I know the PIN code.

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It was her ex’s birthday.

I found out by pure chance.

When Karen’s phone vibrated, I took it back out, seeing “Yoko-senpai” displayed in the notification.

“Yoko-senpai” is my senpai at my part-time job.

You don’t know Karen, do you?

And when I opened the messaging app, the image on the screen was identical to what I had just read about.

It was a love hotel.

As of right now, Karen was taking a shower.

I put on the clothes I had taken off and left the hotel we were in.

On the way out, I typed—

[I’ve got something to do.
I’m leaving.]

Instead of heading directly to the station near the hotel, I wandered aimlessly for a while.

I didn’t know if I could control my emotions after seeing those conversations and seeing Karen’s face as she came out of the bath.
I didn’t know what I would’ve done. 

Would I question her, would I cry out, or would I violate Karen?

That was the reason why I left the hotel alone.

The shock was still stinging in the back of my consciousness.

Something was going on in my head.

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I was woozy, as if I were in a dream still.

…Yes… I hope this is just a bad dream…

But deep in my mind, I knew that this was not.

It’s reality.

I—Yuu Isshiki—am a freshman in the Department of Information Engineering, Faculty of Science and Technology at Johto University.

My girlfriend—Karen Mitsumoto—is a freshman in the Department of English and American Literature, Faculty of Literature at Johto University.

I was cheated on.

The other party was my senpai in high school, college, and clubs—Tetsuya Kamokura.

It was an indescribable feeling, as if my heart was about to be torn apart, only to find that it was completely hollow.

Before I knew it, I had arrived at the bank of the Edogawa River.

The cold night breeze gently danced across the surface of the river and blew on my face intermittently.

But it was just perfect for my burning head.

I sat down and stared absentmindedly at an arbitrary point in the distance. 

…Kamokura, you bastard.
What the hell did you do to Karen? You already have such a beautiful girlfriend…

Tetsuya Kamokura’s girlfriend—Touko Sakurajima—is a sophomore in the Department of Information Engineering, Faculty of Science and Technology at Johto University, just like the two of us.

Tetsuya Kamokura, Touko Sakurajima, and I, Yuu Isshiki, all came from the same high school, go to the same university, and even are in the same department. 

Since high school, Touko-senpai has been well-known due to her beauty.

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She was the head of the literature club and a member of the library committee.
Naturally, she spent a lot of time in the library, so much that she had been called the “Goddess of the Library”.

After entering university, she was nominated for the “Miss Johto University” contest, though she turned the offer down. 

It was said that she would, without a doubt, win if she had entered.

Touko-senpai is not only beautiful, but also elegant in a ladylike way.
Extremely talented as well.

She is intelligent, not stubborn, and strongly self-determinate. 

Just like everyone else, I admired her.

In the second year of university, Touko began dating Tetsuya Kamokura, who was one year older.

…Does Toko-senpai know that Kamokura’s having an affair with Karen…?

I felt a sudden surge of frustration and anger swelling up in my chest.

I can’t let this go on.

Such thoughts dominated my mind.

I pulled out my phone and selected “Touko Sakurajima” from the contacts list and called her. 

After about three rings, she picked up.

“Yes?”

I spoke.

“Touko-senpai.
Please have an affair with me!”

(TL: NTR!)