So there was a council of Nicea. It produced creed and said nothing about proceeding of Spirit. The there was Constantinople which started as regional council and said that Spirit proceeds from the Father. Few yerars later there was council of Rome which said that Spirt proccedes from Father and Son.
HUGE DISCLAIMER
Greek text of the Constantinopolitan Creed of 381, the term "proceeds" (ekporeusis) had a specific and all-important meaning. It meant to originate from a single Source, Principal, or Cause (aitia in greek principium in latin). Latin version of the creed never had that meaning. Instead it use "procedit" as "proienai". Morover to say that Father is not alone principium of Godhead is heresy accroding to Romans.
/HUGE DISCLAIMER
Then, mianly against the arian and semiarian infuluence council of Toldeo started to officialy use creed with "Filioque". Then came Franks and started to due the same but Pope for the sake of unity with greeks (who acted like chuvinist retards i.e. "everything have to be done and speak as we do it") siad to stop with it even though he belived that filoque was ture. Meanwhile Romans sended translation of thier creed to the East but they translated "procedit" as "ekporeusis". Greeks were like wtf but St. Maximus explained that Latins do not mean that anyone but the Father is attion.
Then comes Nicea II and surrundings, Greeks sign the creed with filioque in it. Then comes Great Schism that was and countinues to be clusterfuck. Filoque was made into scapegoat by the greeks.
Then comes Lyons, Greeks yield but said fuck that few years later.
Then comes Florence. And Greeks again act like retards, here personificated in the person of Mark of Ephesus whose whole arguments can be sumarised with this sentece of his (quote actually but you get the point) "There is one source of the pre-essential Godhead –God the Father."
And if you read the Disclaimer then you would know that Latin already do believe that. So John the Montenegro, who was probably as tried of this bullshit as I and countless catholic are, said formally in hope of getting things as stright as possible. Read cautiously for this is what Rome belive about filioque: "The Church of Rome does not admit of two principles or causes in the Trinity, but only one cause and one principal, anathematizing all who think to the contrary."
Florence was absolute bloodbath for Greek argumentation (and pride). To quote Greek who attended it, John Bessarion: "They [the Latins] brought forward passages not only of the western teachers but quite as many of the eastern… to which we had no reply whatsoever to make except that they were corrupt and corrupted by the Latins. They brought forward our own Epiphanius as in many places clearly declaring that the Spirit is from the Father and the Son: corrupt we said they were. They read the text mentioned earlier in Basil's work against Eunomius: in our judgment it was interpolated. They adduced the words of the Saints of the West: the whole of our answer was 'corrupt' and nothing more. We consider and consult among ourselves for several days as to what answer we shall make, but find no other defense at all but that …We had no books that would prove the Latin texts to be corrupt, no Saints who spoke differently from those put forward. We found ourselves deprived of a just case in every direction. So we kept silent.".
Thorically Shism was healed but as soon as Greek left, they break all thier promises and declarations. So we had enough. And ever since when it comes to union with local EO churches (like one in Brest with Ruthenians) we are sattisfaied with "Accept that Filoque is not heretical and we won't force you to even try to understand it.
Here, history of filioque. I may have omitted few thing due the lack of knowledge of subject but I had hit major points. What I did omitted for sure is something irrelevant - canons of councils that anathemise those, who add to creed of NICEA. For at Nicea nothing was spoken about proccesion of Spirit.