No. I don't think helios deserves forgiveness coz he as well had a small role in opposing the abdication of diana essentially. They both played a crucial role along with kael in ruining hes' revenge plan. In a way, I cannot forgive kael lowkey but I understand how he just wants to be happy with the people he loves without getting involved in the Royal drama. Still, the novel would rank pretty high in my list of novels with unsatisfying revenge endings.
I'm not talking about how he also disagreed in deposing diana. I meant he caused less damage to Kael. Iirc his only sin was to abandon Kael (?) when he went and married that btch saintess, plus he realized his faults immediately after he learned how much Kael suffered, repented, apologized and everything, so unlike that hypocrite who ridiculed and criticized Kael's decisions even tho it was for her and for justice, saying like Kael is immoral and she doesn't stand by that bcs that's a sin and goes against her g.o.d, used and abused Kael then abandoned him. She didn't even realize all her sins and faults, she truly believed she's in the right and that everyone who has different beliefs from her are all wrong and bad people. She believed she hadn't done anything wrong especially to Kael until the very end. So compared to diana, Helios is a much better person, he made mistakes, he admitted it, apologized and redeemed himself. So that's why it was much more unbearable to see Kael forgiving diana and disapproving of deposing her as she's done a lot more damage not just to him, but also to Hes and to other people also.