There have been many discussions about breathing patterns on this forum, one at least of which got rather heated, but breathing is one of the most interesting elements of freestyle and also in many ways one of the trickiest.
I have always been a left side breather since learning to swim front crawl thanks to Terry's first book, and over the last few years I have been trying to incorporate alternate breathing into my stroke with a modicum of success. I still breathe to the left for preference but can now breathe to either side with relative ease if I have a little time to think about it. I have found that breathing every three strokes is difficult for me and every five is easier, although I can't sustain the every five pattern for very long. Over a single length of a 25M pool I can breathe every five, every seven or sometimes every nine, or even every eleven, but after the turn I cannot sustain these patterns and have to revert to more frequent breaths, sometimes managing some breaths at every three. I expect that eventually I will be able to breathe either side at will. I think the exhalation is the really important part of breathing and the right side breaths seem to come easier if I have fully exhaled or almost so. Breathing to the left does not require any real thought, and often happens unintentionally, while breathing to the right requires the intention to do so and focusing on the right hand as it spears forward. I imagine that everyone has a slightly different approach and perhaps some necks are more flexible than others, but in my case it seems to be more a matter of ingrained habit.