I might be crazy but I think that the takeaway might be that Shuuten Douji actually liked him and Ibaraki should go fuck him in the ass?
Like I think the idea is that up until now Shibaraki believed everything Shuuten Douji told him, including A: that Shuuten Douji never loved him and B: that Shibaraki was only good with his ass (which apparently implied that he wouldn't enjoy using his dick.)
But then succubus girl proved that using his dick feels awesome, which means that B is false, which means that Shuuten Douji might also have been lying about A. And then everyone tells him yeah A was definitely a lie.
So yeah I think the conclusion is that he should go split Shuuten Douji in two.