It should be pointed out that the Filioque was accepted by 2 Ecumenical Councils in which the Eastern Churches took part:
We confess faithfully and devoutly that the Holy Spirit proceeds eternally from Father and Son, not as from two pronciples but from one, not by two spirations but by one only. This the holy roman Church, the mother and teacher of all the faithful, has so far professed, preached, and taught; this she continues to hold, to preach, to profess and to teach. This is the unchangeable and true doctrine of the orthodox Fathers and Doctors, both Latin and Greek. However, some have fallen into various errors out of ignorance of the above indisputable truth. Therefore in order to forestall such errors, with the approval of the holy Council, we condemn and disapprove those who presume to deny that the Holy Spirit proceeds eternally from Father and Son, or who rashly dare to assert that the Holy Spirit proceeds from Father and Son as from two principles, not from one.
The Second General Council of Lyons
Constitution on the Blessed Trinity and on the Catholic Faith (1274)
In the name of the Holy Trinity, Father, Son and Holy Spirit, with the approval of this sacred universal Council of Florence, we define that this truth of faith must be believed and received by all and that all must profess; the Holy Spirit is eternally from Father and Son, he has his nature and subsistence at once from Father and Son; he proceeds eternally from both as from one principle and through one spiration…
…Moreover, we define that the explanatory words ‘Filioque’ have been added in the Symbol legitimately and wityh good reason for the sake of clarifying the truth and under the impact of a real need at that time.
Reunion Council of Florence
Decree for the Greeks (1439)