How they could react when they see their S/O cheating on them? (Like... in the street)
Eren doesn’t know what to do, honestly. He’ll probably watch them for a while, trying to be super stealthy so they don’t notice. He won’t believe it until it’s unavoidable. If they’re in a private enough space, he’ll confront them then and there. If they’re in a super crowded public place, he’ll wait until they next time they meet up and ask them what that was about. He won’t beat around the bush either, getting right to the fact that they’re cheating and that means their relationship is over.
Mikasa would be so shocked and hurt that she would refuse to talk to her S/O for a day or two, with no explanation. And the next time they do talk, it’s a phone conversation in which she tells them what she saw. That conversation either ends in a break up or a meeting date to talk it over (which still probably ends in breaking up.) She doesn’t give them a second chance. Once you’ve broken her trust, you’re out.
Armin won’t approach them then, but will be super touchy the next time he sees them. He might keep his knowledge to himself for a while, but he won’t be able to hold up for long, and will tell them what he saw without accusing them of anything. He’ll just bring it up and wait for them to come clean on their own. If they don’t, he’ll pry. He knows what he saw, but is willing to give them the benefit of the doubt. But he’ll never really trust them the same again if he doesn’t break up with them (which there’s only 2-5% chance he’d stay.)
snk stickers! you can buy them on my redbubble here (x) in these groups or just one character by themself, and I’m gonna add more combinations than just these ones (like levi & eren together, mikasa & annie, etc)
I might make some more of side characters like petra, marlo, zeke, and whoever else, if anyone wants!