as stated in the description this story revolves around a couple that broke up and is reunited by fate from what I get from reading this was that our MC is just a typical guy that likes to read books and our overwhelming innocent fMC who is easy going and free spirited in the first chapter introduce us to Yuzuru (mc) and to Odaijima (supporting role) they are discussing the transfer student in which is Mizuno (fmc) the ex girlfriend of Yuzuru welp since it still the start of the chapter he don't know whats the name of this new transfer student in which when he heard the name of our quite energetic female main character he said that it was the same name as his friend after this little conversation Yuzuru coincidentally found Mizuno and basically said hi in which triggered a flashback about them and basically you'll know it after reading after this little flashback from what I recall after this conversation after a few days while Yuzuru is home Mizuno Came to visit him and basically asking Yuzuru to take him and basically stroll around and remember the past and I remember after this scene a flashback played and basically said the reason about why they broke up after this scene ends we have been introduced to the "rival" his name is Ando the normal popular student that I do believe everyone has meet in school and probably interacted with. He basically wants to date Mizuno so he Goes to Yuzuru and basically "asked are you guys dating?" in which Yuzuru answered "no" which would basically give a sign that he is perfectly fine to pursue a single girl and after a while a sudden downpour occurred we got ourselves an conversation of Odaijima and Yuzuru in which I forgot what was it after this conversation as Yuzuru is already near his house he saw Mizuno basically wet and is standing on the rain without cover and I will not spoil what happens next after this they basically start, the beginning of their love story.

since they basically started at the beginning again

As 30exp mentioned, she's easygoing and free-spirited, a little bit too much so. To paraphrase another review which sums it up pretty well, the MC (whose character is pretty decently written out) is deeply attracted to the free-spiritedness of the FL, but after dating, realizes that if you fall in love with someone like this, you cannot keep them locked up forever. If the MC tries to change the FL, then the FL wouldn't be the same person he fell in love with.

From the FL's perspective, she has found someone who understands her, but she does not realize that there is a difference in expectations in how much she can do as she wants and because of this, her actions are hurting the MC. This is why they broke up at the start of volume 1.

The FL goes on a date with the MC's best buddy but denies it saying that they just went out to play and that it wasn't a date. At the same time, although they like each other, the MC and the FL haven't been officially dating yet so you could say that the FL has the discretion to do what she wants. You can decide whether you can accept this, but I think most reviews regarding this point were from people who got PTSD from Sayu Ogiwara from 29 to JK.

For me, what left a bad taste in my mouth was that the MC was always left hanging on dates, and he was deemed to be childish when asking for an explanation.

Vol1: Is about MC Yuzuru and FL1 Ai reuniting after they broke up in junior high. "Free-spirited" means that Ai is someone who kind of does whatever she wants; sometimes at the expense of Yuzuru (i.e., cancles dates / breaks promises in favour of doing something else she just impulsively decided on). Yuzuru got fed up and broke up with her. Vol1 is about talking these things out and becoming friends again; so that's the 30exp's review; the story ends by returning to the prologue. Note, Vol1 has a lot of foreshadowing with FL2 Kaoru; indicating that she too was close to Yuzuru.

Vol2: Is about Yuzuru and Kaoru, Ai acts more of a support and Yuzuru became more proactive after facing his personal issues with Ai back in Vol1. Not much time has passed since then but Yuzuru does not want to regret things anymore, so he became more proactive. Vol2 is about Kaoru and her family issues and Yuzuru gets involved because he genuinely sees Kaoru has a friend; though Kaoru may want something more than that. In Vol2, the same title 'You are my regret' refers to Kaoru's regret, not Yuzuru's. Note, Vol2 has a lot of foreshadowing with FL3 Risa, a girl with piercings and cuts her arms.

Vol3: Is about Risa and the guy who tried to steal Ai in Vol1. It was weirldy paced, starting off with a beach episode but then went into a music/band arc, with MC becoming the drummer. He practiced at Risa's place and learned more about her and her family situation. There was subtle foreshadowing about Ai's family situation. Risa's drama is resolved in the end and the volume ends with a cliffhanger, with Ai's sister telling Ai to return home. So Vol4 will likely be about Ai again.

Well Risa's drama was more about regaining her passion for music and stuff but it's family related since the reason why she stopped music was because her father killed of his girlfriend, both father and that girlfriend where kind of like Risa's parental figures. The real mom just left.