The fact that Fuutarou thought it was Rena is a nice recollection of how he first met Yotsuba all those years ago in Kyoto, when he was sitting at the bottom of some stairs and she came from above to help him.
Also there is still Itsuki left(unfortunately, I could live without her) and we don't know how will that one go, but the fact that Fuutarou has no idea who kissed him this time, actually gives Yotsuba bonus points to uniqueness, so I still have my hopes up.
The crying scene had me a little confused at first, but if it is to show how hard it is for Yotsuba to let go of her love of past 6 years, then it really leaves an impact.