I noticed a few things in chapter 134.
First, Sakura is actually capable of getting angry and arguing with that playboy, so why did she just stand there silently before while the blonde and the playboy badmouthed Shinobu? Was it because Sakura herself was dissatisfied with Shinobu at the time, and those people just happened to say exactly what she wanted to hear?
As for Shinobu, he feels like he doesn't want to see Fumi get 'intimate' with another guy, even if it could boost his own reputation, which proves that his love for Fumi is not shallow.
It seems Sakura and the playboy have a relationship, but they aren't living together; the formal way Sakura stands and talks to him feels like an employee meeting their boss. The apartment is actually quite small, seemingly just for one person, and Sakura doesn't look comfortable, like it's not a 'this is my home' vibe at all.
Regarding Fumi, her insecurity is totally justified—when you love your boyfriend too much and know that he once had deep feelings for his ex, it's completely natural to lack confidence; in this case, all it takes is for Shinobu to talk to her and give her that reassurance.
As for the sex scene offered to Shinobu, what's under the blanket isn't what everyone says—like the two actors having to be completely naked and the male actor taking advantage of it to have sex with Fumi. In reality, both actors might wear pants and only expose their upper bodies, with Fumi wearing a skin-toned strapless bra. It's simply that Shinobu doesn't want to see Fumi being 'intimate' with anyone else.