Itsuki was doing a search on Romance issues to try to understand why Ichika is planning to leave... She is thinking it has something to do with Fuutaro.
Also, I am not sure why you say Fuu and Itsuki's relationship is so balanced and trust base... there relationship started far from trust base... even Ichika noticed it here even though by 91 chapters it's probably different by now.
I personally think that their relationship is "balanced and trust based" because the amount they give and receive towards the growth of their relationship is just about equal. Unlike the other four and especially Miku whose happiness is dependent on Fuutarou.
This was probably my favorite chapter by far. Our MC is showing active interest in the quintuplets, which is something I can't say about the previous chapters. Maybe we'll finally get some development on the MC's side on how he fell in love with one of the sisters.