my parakeet flew into a close window twice...?

Keep an eye on him and if anything seems wrong get him checked out. From now on when he has out of cage time, cover the windows so he won't try to get through them again. I'd invest in some good blinds for the windows so you can have them shut only when they need to be. Also, you might want to clip his wings. There are ways to do it that only decrease their flight abilities instead of taking them completely away.

If you clip them in a way that does that, he'll still be able to fly and get away from things, but he won't be able to get as much speed and length into his flight (which is good because then he has less of a chance of getting hurt when he tries to fly into something hard) . Just make sure you don't clip them in a way that does take his flight completely away.

Clipping birds wings is cruel. They need to fly for their physical and mental wellbeing.. Birds that aren't allow to fly tend to become overweight which is not good for their health. Birds don't understand glass so when keep in cage and give daily free flight you need to have nets or something up or close the curtain.