From the very first chapter on this has been heavily implied. Himmel was a true GIGACHAD, who knew his wish couldn't come true, thus he settled for the present - since the future was unattainable, and would have been ultimately cruel to Frieren."An idyllic dream that one has already abandoned"
Himmel already knew he would never be with Frieren![]()
He chose living his life with no regrets and enjoy the adventure he had with his friends, or rather the most important people in his life.