C'mon people, MC doesn't give a shit about "senpai". Only in this chapter they implemented that idiocy of "I'm gonna help her" after she touched every last inch of her body. How would you get close to your senpai if you never actually cared about her? The only thing she wanted was fucking her, that's all, only this chapter she seems to remember Seto is not just a pair of boobs and a pussy, but also has a brain and feelings (assumed).
Morals apart, mc never gave a shit about real senpai since the beginning, and now in her adult self this has only worsen.
You can want to have sex with someone and care about them at the same time. Acting like they're mutually exclusive is honestly weird to me, and this chapter even ends with the MC wanting to help the Senpai's acting career. After remembering being sadden and frustrated with how her Senpai felt defeated and gave up. The MC very clearly cares about her.
Absolutely not weird, one thing doesn't necessarily come with the other and also the other way around, but if she sometime really cared about her senpai (sentimentally), now that interest is totally gone, and I can't see where you see she "clearly cares about her", you mean like in those scenes she groped her breasts, stoled her a kiss or smell her ass? If she really cared, then the first thing she should've remember was that her senpai wanted to be an actress (that is, apparently, her dream, goal in life; I guess that's maybe the most important thing for a person?) and that her failure led to her lately unhappy life.
This "I'm gonna help senpai" only resembles the sudden plot change in joshikou dakara safe from a teasing (bullying) romcom to a love triangle, square, netorare, what? Author obviously saw this kinda thing wasn't going to work, same as JDS initial plot, and decided to add some depth to MC, and I don't complain, finally she's gonna be any different from a simple molester, but you can't tell she was a profound character since the beginning or that she wasn't totally disgusting all along.