It's understandable Karel didn't believe Sasya's love because from the beginning he knew that his love to Sasya was one-sided love. While Sasya developed his love for Karel without being told. At the end of the story it was revealed that Sasya had suffered a lot even not as much Karel who was sent to the battlefield but it was a heartbreaking.
Oh poor sasya. Where did you read the novel? But I might also add even if sasya been through alot it was based on a more self centered reasons while karel was serving for a crime he didn't commit to get back to someone who didn't wait for him (which made him feel unlovable and unwanted)
I didn't read the full novel but asking someone about the whole plot. This might contain spoilers... Actually Sasya had waited Karel. He sent the letter to Karel "To my beloved Karel, I'm leaving france. let's meet again there. I hope i can be someone worth for you-Your Sasya". While he knew Karel was away, he didn't want to stay alone (don't forget Sasya was a broken soul) so chase his dream to become someone that Karel would be proud of. But Karel didn't get the letter so he assumed that Sasya's absence was due to his ambitious and greed especially the news about him sleep around to get his position (which not true. He seduced them but he didn't sleep with them). All because he wants to be success before meet Karel again. Unfortunately Karel mistaken about it and also the news about Karel's death torn Sasya apart because he waited Karel for so long When they met again as Skar, Sasya was hoping to atone all even none of these was his fault. Instead Karel coldly treat him and humiliate Sasha. He was broken hearted.
"He has no regrets cause he purred all his love for me and I have because I didn't"
EXACTLY. I feel bad for sasya but karel has been through so much to just give in to sasya after all that. On top of that he doesn't believe sasya's feelings for him as ever been genuine