When the vocal cords are pushed apart because too much air is being forced through them, they can't vibrate together as they should, and therefore, your voice is weak and breathy. So you compensate by straining to make more sound, ending up with a harsh sound, and ultimately a damaged voice.
To get rid of that breathy sound, simply think of 'aiming the sound BACK' rather than pushing it FORWARD with a lot of air coming out. I talk a lot about this in my book From Shower To Stage....7 Easy Steps for Singing Like A Pro! and you can also see a demonstration in the video below.