How would you make Todo react when he finally learns just what a huge, cruel joke that entire thing with Mido was? Do you think he would be furious with those kids he never knew? Or horrified? Or would he be hurting for Izuku above all? What would his first thought be? I imagine him gently cradling Mido's gorgeous face and then hugging the life out of him, and then giving him the sweetest kiss he's ever known. Your writing makes me think things, how dare you be this good.
Once he gets past the confusion he’d probably have a knee-jerk anger reaction on Izuku’s behalf. And he does voice his first thought in the fic: “Why would anyone joke about being in love with you?”
Because he’s completely gone for Izuku at this point, and those feelings (and Izuku himself) are incredibly important to him. So, the thought of someone turning that into a joke, to the point where expressions of love actually cause Izuku pain, is not only repulsive to him, but just plain doesn’t make any sense.
And knowing this, I think he’d put extra effort into showing Izuku that he is loved, and it’s not a joke. Of course, he’d show it in his own awkward, emotionally floundering way (he’s trying, okay, he’s bad at this but he’s trying) but the message gets across just fine.