Close gap between bathtub border and wall

Question

In my bathroom, I have a bathtub with a showerhead. The bathtub is diagonal, one side is a semihigh wall, behind is the toilet. The other side is attached to a wall. Problem now is that there is a gap between the upper border of the bathtub and the wall. When I shower, then the water runs there and on the floor, which is annoying to clean. Attached some pictures, because I find it hard to explain. How can I close the gap in a way that I still can remove it easily later? First thing I did was putting cloth on there, but after a year it rotted. Right now, I use some bottles to fix the shower curtain in place, but the curtain now also rots a bit.

Answer 1

It's a bit hard issue to handle, because, as @isherwood indicated, that tub's destiny has been changed.
I can think of two groups of 'fixes' depending on how much You are motivated:
a. change of usage - bathing while standing must go, fix the shower head lower, try to use it kneeling or so, check if sutiation changes, consider using the tub as a bath tub
b. change of environment - consider changing the cloth, but this time let it start under the showerhead to let water be gathered by it before it reaches places You want to avoid getting wet; this must include change of cloth's suspension