I don't like the writing of this. Most of a chapter of "they're the ones in the dog video" which would have been hilarious if Nakahara Aya did it but in this mangaka's hands was not, two pages of actual plot which seems to be the entire explanation for why we had this whole timeskip-to-post-breakup-and-then-back sequence, and only one incident of the two leads actually getting closer (hug and whirl) which wasn't enough to give me much feeling that these two had enough of anything going that I should be feeling bad about them getting distant. This whole manga has been brimming with missed potential. It all could have been so much better than it is.
I will say this, though--the actual reason everything went sour was lame in a completely believable "Yes, this is the kind of lame reason people can ruin their relationships" sort of way, and also very true to that girl's character. She's fiery, impulsive and bad-tempered and said something totally bitchy that she didn't really mean, and is totally the kind of person who would then have that weird combination of stiff-necked pride and major guilt that wouldn't let her say sorry or get past it. The moral of the story being, if you act like a douche, say you're sorry.