Long ago, but later than the Latins think (they'll date that to the original break with Rome) and longer ago than most, who fancy it was the embrace of homosexuality (not mere tolerance of, which would be bad enough) or the priesting of women, would suggest.
They jumped the shark when they couldn't condemn "Bishop" Pike for heresy when he denied the Trinity, deciding instead that "heresy is no longer a relevant category" (which in theological matters is equivalent to deciding that truth is no longer a relevant category). Yeah, that was the U.S. bunch, PECUSA, but the Lambeth Conference didn't slap them down, as they should have, if Anglicanism still stood for (even a solid approximation of) the Faith once delivered to the Saints.
The Oxford Movement seems to have been God's last attempt to recall Anglicanism from a slide into apostacy. Now most of the Oxford Movement's spiritual descendants are either Orthodox or Latin. So, be not downcast, you can still check the web for times and hear a good sung Evensong and not have to deal with rank apostacy by turning up at an Anglican Ordinariate parish or most Antiochian Western-Rite parishes.
‘Don’t despair’ — we won’t. We ran screaming to the CC.