Intentions are very rarely the determinant of boundary crossing. Most people in relationships or in marriages rarely go to work or to a company dinner thinking about cheating on their spouse and yet by large, most affairs occur in the workplace.
I digress. What most people are freaking out about is that the MC is clearly attracted to his ex. It could be argued that this level of attraction might be in actuality something more akin to infatuation. The MC’s reaction to the picture profile of his ex is a perfect example of how much he still likes his ex. Despite being in a relationship and knowing that saving a picture of the ex isn’t acceptable (indicated by how he’s questioning how he could get away with it), he still considered it.
What does that tell us? The MC is willing to do something that he wouldn’t normally do for someone else. He’s crossing boundaries. A big red flag. He’s creating this secret emotional intimacy with his ex which while is in its infancy, can still be considered an emotional affair.
Now we need to see if he’s going to inform his partner of this meeting with his ex. Which assuming by the title of this manga and what the synopsis is telling us, he’ll likely cheat on his partner. That dinner (which could’ve just been getting coffee together) is most definitely the catalyst that’ll begin the affair.
*The fact that this is the MC’s first love is another can of worms that I won’t divulge in right now.
Guys going out to have dinner with an ex is not cheating