The Catechism says that Pope St. Leo–whom I believe the Orthodox recognize as a saint–dogmatically confessed the Filioque.
I’ve never understood why this is a Church-dividing issue. From my limited experience in talking with another Orthodox person, I found that the issue was partly just semantic. When the Orthodox guy said “cause” he meant exclusively the primacy cause, and thus only wanted to use this word with reference to the Father. Whereas I understand “cause” as something that can refer to a secondary cause, such as the Son.
Clearly there is a difference in emphasis which is beautiful and legitimate.
The North-American Orthodox-Catholic Consultation made an agreed statement on this which I read some years ago and found helpful
usccb.org/beliefs-and-teachings/ecumenical-and-interreligious/ecumenical/orthodox/filioque-church-dividing-issue-english.cfm
They cited St. Gregory of Nyssa:
"Gregory of Nyssa, for instance, explains that we can only distinguish the hypostases within the Mystery of God by “believing that one is the cause, the other is from the cause; and in that which is from the cause, we recognize yet another distinction: one is immediately from the first one, the other is through him who is immediately from the first one.”
usccb.org/beliefs-and-teachings/ecumenical-and-interreligious/ecumenical/orthodox/filioque-church-dividing-issue-english.cfm
Now that is what I believe as a Catholic. So I don’t understand the division over this particular issue.
Lastly, my opinion is that there will be a re-unification, but that many Orthodox will reject it, many or most of them in good conscience.
That’s my two cents.