I feel like it was more when like claude was shown to be better than his bro in terms of magic or idk. So I guessed he felt inferior to his little bro, thus, from then the relationship went down. I think it was stated in the earlier chpt, I think in chpt 23.
Dude RAEL’S BLUSHING FACE OH MAH GAWD I LITERALY SQUAKKKKKED but like dude the knight is so hot wtf lmao share