Should a toilet be flushed after every use?

My boyfriend won't let me use his bedroom toilet anymore because I keep flushing it after every time I use it...He said I should only flush after every 3rd time I use it. Unless its "number 2"...I told him that its disgusting to leave "peee" in the bowl and not flush but he keeps arguing that its only "water" and we should conserve the water...So now he won't let me use his bathroom in his room unless I only flush after the 3rd use...I find it sick and unhygienic...What do you think?