hi, this will clarify the subject of breathing, I used to try to breathe through the nose ALL the time, what ended hapening was that I wouldnt be able to do it, (sing with ease) why? because if lets say, you are singing a fast song, you dont have time to breathe through the nose, just right now try to breathe as fast as you can through the nose, youll see, what happens is that your nostrills will shut and you wont be able to breathe correctly as if you took a slow breath through the nose, you should be able to breathe through the nose without hearing the sound of the breath, thats how it should be done the right way, I always joke around that if you breathe really fast thorugh the nose youll end up eating your buggers haha because that´s what will happen!!!
so I always post this video of Pavarotti singing nessun dorma, youll notice he breathes through the nose when he has time, and when he doesnt have time he breathes throuogh the mouth, this is the best way to think about this
so by now watching this you notice, this is why we should study phrase by phrase. and then try a whole verse (just like a guitar solo) then verse chorus, even with a sheet of paper and write down what we really be concious of.
example first line of the verse: through the nose, second line can I do it? try , no? through the mouth, next part can I? yes ok through the nose....
this way youll propgram yourself to do this right
hope this helps