I've been having troubles with my bougainvillea recently. A few months ago, it started showing signs of iron deficiency and I learned that periodic application of diluted liquid iron helped to get its leaves back into color. But a few weeks ago, its leaves started to curl and turned slightly yellow on the entire plant and now it looks like in the second picture, except for this guy on the back of the plant, this one branch, which looks like this (1st photo).
I do not overwater, the soil dries out fast and the plant is fertilized. I keep it on a terrace, which faces south with plenty of direct sunlight (I already got it inside, because our september/early october weather is worse than a november one here in Central Europe). I don't know what else I can do I think it maybe has to do something with roots, or some bacterial disease? I don't really know. The plant has been showing signs of distress long ago before I pried it out of the hands of my mom and tried to keep it alive (and it obviously needs to undergo some pruning).