Do you open the window to help the air circulate when it's hot? Also, sounds like it's getting too much water? That's my only guessing.

Here in sandy Florida we let ma-nature do all the watering for our bougainvillea. We get better bloom when it is dry. I would hold back on the water.

I agree, they love being dry especially while indoors. I think I might have watered mine 2 times the entire time it was indoors. It had a bad case of spidermites, but stayed alive. Now its outside getting a little more water, but it dries out because that encourages flowers. Mine also dropped a lot of leaves (to the point where it had almost none left) when it first went inside for the year, but it recovered really fast. They really hate being introduced into a new place, but they get used to it.

Good luck!

Okay, mine will refuse to bloom most of the summer when outdoors (exposed to full sun, high heat, fresh air, and rain). Then I bring it inside to a bright, western exposure and basically forget about it over the course of the winter and it blooms heavily in January and February.--DO NOT pamper this plant! Don't over fertilize or over water it. They LOVE a certain degree of...neglect, and will reward your seeming cruelty with flowers! You can't burn this plant.--They love heat, drought, and sun.

Its hard to neglect a plant that has the potential to look so beautiful, but it really loves to do its own thing. My goal this summer is to neglect it and see how it goes. It was still small last year so I had to give it lots of fertilzer so it could gain some size, but now its a good height and ready to put on a show.
Dont worry if things look bad. In the short time I have had mine (not even a year yet) it has almost died 2 times.

Thanks everybody! its going back on the windowsill. i do open the window but there's not much circulation in the back