The general rule of thumb is that if you're using the suit in chlorinated water, you should get about 60 hours out of it. At that point, the chlorine will likely have striped the fabric of its structure and it will collapse' - the fabric will seem to give way, particularly in the butt area. Rinse, rinse and rinse. After every practice, rinse your suit well in fresh water. Ideally wash it in soap that's specially designed for swim suits and fine washables.
Regular detergent can harm the fabric, making it go even sooner.
Never machine wash or dry your suit. Some shampoos are fine - as long as they're the type designed for removing chlorine. Regular shampoos have ingredients designed to soften your hair. If you're going to use a regular shampoo, use it after you've removed your bathing suit and don'tuse it on the suit itself. It's common to see suits being wrung out to remove water, or being looped through locker handles to dry.