Maybe I need to reread it again cause I kinda don't get the story.

The uke was in love with his senpai who was married to the professor. She introduced him to the music, and then she invited him to go to a concert with her but he declined because he had to do something with the prof. Then she died, and there was a thunderstorm that day so he now has a phobia of that. The uke blamed himself, and the professor propositioned him because prof knew that uke had a crush on his wife.
And that's what happened in the past. IDK how to spell their names so yeah. Hope this was clear enough.