In the 1180s the Empire was governed by a French princess (regent for her son) and her late husband was very pro-western/latin. The relations between the Catholic crusader states and the Byzantine empire were also very good and Italian merchants controlled most of its economy.
Then.. an anti-western emperor came to power had all the Latins/Italians in Constantinople massacred (>10% of the population) and things went pretty much downhill from there. It was very rapid, though. There were of course disagreements before the late 12th century but both sides generally acknowledged that they were part of the same Christian word/universal empire (even if they didn't quite agree who was in charge).
Then.. an anti-western emperor came to power had all the Latins/Italians in Constantinople massacred (>10% of the population) and things went pretty much downhill from there. It was very rapid, though. There were of course disagreements before the late 12th century but both sides generally acknowledged that they were part of the same Christian word/universal empire (even if they didn't quite agree who was in charge).