Competetive swimmer as well - always breathing every second stroke. When competing in 50 meter distance, I don’t breathe at all (once at the turn). When I swim in open water, like 2-3 km, constant pace without rest, it’s every second stroke. If I breathe every third, I’m always slightly out of breath.
The most interesting question for me is not when to breathe, but when to swim with symmetrical strokes and when to swim with asymmetrical. For me, it’s symmetrical in still water - asymmetrical in waves or when sprinting.