The main differences are in their expressions and some minor details of personality. In the manga, Deku might seem a bit more intense, while in the anime, he's sometimes presented a bit softer.
Deku might be completely shocked at first. Since Bakugou has always been so aggressive towards him, he would never expect such a confession. He might just stand there, mouth agape, not knowing what to say.
His friends could come to the rescue. Bakugo, for instance, might use his explosive power to break into Toga's hideout. He's always been competitive with Deku, but he also cares about him deeply.
There could be. Fanfic writers are known for their creativity and often come up with unique crossovers. 'Dark Naruto' is an interesting take on the Naruto character, and if combined with Ganon from another universe, it could make for a really engaging story. But to find it, you may need to explore different fanfic archives. Some fanfic writers might also post their works on personal blogs or Tumblr pages, so it's worth looking into those as well.
He might cry a lot. Deku is very emotional, and being cheated on would be a very painful experience for him. He could also get angry, which is rare for him, but this situation would be so unjust that he might not be able to hold it in. He'd probably start to question his self - worth too, thinking that there was something wrong with him that made his partner cheat.
In the manga, Deku's speed isn't constant. It improves as he gains more control and power. For example, in intense battles, he can move at impressive speeds to outmaneuver opponents.
Deku's speed varies depending on the situation and his development. Sometimes he can be incredibly fast, especially when he uses his special abilities.