WHO

after what i understood, eren was the mate - but they didn't know, well idek, but just a guess

It was stated that Armin is a beta and eren isn't levi's mate. Levi found his mate and didn't even have sex with it even tho it was in heat because his love for eren won over his instincts. (▰˘◡˘▰)

aww, how cute

Ikr! I can't believe I found this manga so late ╥﹏╥

From what I understand, Armin was Levi's mate. Levi rejected Armin cause he loved Eren.

Hanji said "Levi's mate contacted me and said it was good the bond was broken"
On the same panel she said that we got a flashback scene where Armin and Mikasa was at her door.
Armin then does on to explain that humanity is changing

his mate was kenny. the guy at the bridge guys. the guy he had a past with, once upon a time, who shares his last name.

Levi’s mate was not shown, so is Eren’s mate. Armin is a beta, he doesn’t have anything to do with both levi and eren aside from being a very very good friend.!According to Hanji’s data, levi rejected his mate, he still feels the urge to procreate, but he didn’t fall in love with his mate. Eren isn’t Levi’s mate, but Eren also rejects every Alpha other than Levi. In conclusion to what Hanji’s LATEST data on both Levi and Eren, it showed that they have become a fateful pair and have defied their instinct to be with the one they truly loved.

Kenny is levi’s father here and Kenny murdered Levi’s mother, his wife, because she slept with her fateful pair (another alpha)that was why Levi didn’t touch Eren because he didn’t know if he could stop himself if he met with his fateful pair and hurt eren.