No way. The manga portrays their connection through mutual respect and competition in their journey to become great heroes. A kiss is not part of that narrative at all.
Another theme is growth. Both characters grow as heroes and as individuals. In these fanfics, you can see how they influence each other's development, whether it's in terms of their quirk usage or their mental strength. For example, Deku might inspire Bakugo to be more selfless in battle, and Bakugo might push Deku to be more assertive.
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.