Yarashiku Shitsuke Kete Itoshite Ageru -Dom/Sub Universe-
Ai to Makoto (Moriyo)
it's more than black and white in this story. They didn't love each other in a romantic way, it was more of a guilt/responsibility induced situation. Seiji felt guilty because due to his mistake he bit and made Aiji his mate, but breaking the bond would imply hurting his brother and leave him. He didn't want that and the only solution he, a kid who was only seen send pointed for his second gender, came up with was taking responsibility taking his role as mate/partner/Alpha. Remember they were too young, without anyone or support, or someone who taught them well. Aiji knew it was wrong, but didn't want to be left alone so he clung onto him, that's why he said "dragged you down for 10 years" At the end, they're still brothers, so is obvious they love each other but it was made clear it was not as a lover but as his brother and you can confirm that at the final pages when Aiji asks Seiji why doesn't he bites Towa already
My Darling Liar Boy