they're the only one who've said "I love you" to one another, although again this probably won't matter much atp for the final chapter. Only reason why the noice was made is because the dynamic between Sakura and Shinobu was something readers enjoyed and it got burned over a pretty silly sequence of events.
Well that "love" as I've said in an earlier post, seems to be unconditional from only one side.
Claiming that your significant other cheated on you without confirming/confronting your partner, then skimming over the fact that you, too stepped out on your relationship. On top of that, not even confronting your (ex) partner in person and just deciding to break up via text and having her affair partner do it for you.
You can say she feels guilty, but that's it. It doesn't seem she claimed any responsibility - at least partially - for ending the relationship.
...and this is just one of the infidelities committed by her. I'd consider her a sociopath if she didn't at least feel bad about it.
We can blame this on the author, but that declaration seems to have meant something to only one of them.