Ye the incest was annoying, and he hates women because he can't be them
One sided incest, I guess the author wanted to depict a case of "impossible love" since it was apparent that senpai never see his sister romantically. He can't and never want to. Even so the sister was used to show how she still tried and didn't gave up easily even though her love is clearly much more impossible than Touma's.
Touma "hates" women because he was jealous of women, I don't think he really hates them tho. Its more like he is not good dealing with them. Bcuz if he really hates women he wont be friends with senpai's lil sis or gone to his girl senpai's wedding. He is just so jealous with nana chan (childhood friend's ex gf) that he got sick whenever he saw them together. But in the end, although he ignores nana, he never treats her badly.
I guess Touma didn't end up with senpai cuz from the beginning the childhood friend never loves his gf, he has always been obsessed with Touma without realizing he did. And senpai wants to see Touma happy rather than wanting to be couple with him. He probably knows Touma's love runs too deep for him to interfere. And just like he said, it was like he was watching a parade, and he is in love with the person who is involved in an unrequited love of two person.
I hate this, why is there incest??? Why did Touma hate the gf and women in general so badly? And is he really gay? Bc he has some crazy body dimorphism. WHY DIDN'T HE GET TOGETHER WITH THE SENPAI???????