Are you seriously serious there ?! Haruki. Does. Not. Want. To. Have. Sex. With. Hikaru. This is written in every chapters ! The fact that his body is reacting during the rapes - a natural reaction - does not mean he wants to do it. This is so simple to understand !
Moreover, yes, Hanabusa tried to help him but he left as soon as he learnt the truth. When I read your comment I have the feeling you think that Haruki rejected Hanabusa's help and that it's his fault if he's alone now...
But I agree with you on the fact that this story is really good.
Haruki did not offer himself because he can't have Hanabusa. He's given up on fighting Hikaru but he still does not like having sex. All his prior efforts to fight or convince Hikaru have been to no avail so he's feeling powerless. Rather than aggressively fighting back he's giving Hikaru what he wants. He's thinking what's the point in fighting anymore if he's just going to lose anyways. He's not really even thinking about the sex much while it happens. Haruki compared it to when he was slicing the apple and cut his hand.

Is it wrong, stupid and futile of me to keep rooting for Hanabusa-senpai? Why are we not seeing more of him after he ~realized~ what's going on?
SENPAIIIII (╥╯θ╰╥)