well, he "canonically" was. But honestly, I think it's way more complicated than that. He didn't grow up knowing what family love was supposed to be like, and if you think about it, she was the first one that cared about him and that probably confused him since he developed this "love" for her when he was a child, and at that time, he probably didn't even know how to differentiate romantic and platonic love so he just assumed he loved her romantically, and when someone else "took her away" it just reafirmed this idea. But tbh I think he just mistook his feelings due to the childhood trauma and he admired her and wanted her to be by his side forever. I don't even think he had sexual thoughts of her at all since there's 0 hints of that. He just wanted to be with her, I don't think he was actually in love, but it's just my opinion. The teacher was his proper first love ╥﹏╥
Oh word (。･´д`･。)
Fuck me if im wrong, but is he in love with his sister/cousin..?