We will never see Sakura's full train of thought. Like we never saw Iida's. The character would sound completely retarded and/or broken if we did.
Imagine in the last epilogue of Karami Zakari we would've seen Iida's motivation: "hmm, Kousei is getting married so my gift to him is a last scene of me being defiled by many men i barely know because i want to send him off our own way. so i'll be here alone and pumped full of cum while I watch him getting married because, i don't know, something something wanting the hapiness of the one i love."
So what about Sakura? Assuming she has been getting it on left and right: "it hurt so much when he cheated despite the fact that i never even confirmed that is even true. but somehow i let the actor mess me up while shinobu was trying to contact me and now I don't even want to talk to him because now that i stop to think for two seconds it might've been a misunderstanding but it's too late, i don't want to admit that after all he did for me, i jumped in bed with the first guy that put his fingers up my coochie. And now I have to put out left and right because, since i don't have a guy who loves me fighting to get me roles in movies, that's the only way i can guarantee some minor roles in tv dramas. oh, i still love him, but this is who i am now and what i deserve. because picking up a phone and say hi is too much for a young adult like me to do. woe is me."