Over time, chlorine,  salt and sun will damage the Lycra fabric in your swimsuit. However, you can take a few steps to extend the life of your uv swimwear swimsuit.

Wash the swimsuit by hand with a mild soap after every use.
I have found Woolite to be one of the mildest soap for washing you swim wear. Plain water does not remove the chlorine or salt water.

Never wash your suit in a washing machine.
Just gently hand wash it in the sink and hang it indoors to dry. The washing machine will breakdown the lycra and ruin some of the bra cups that are sewn into many swimsuits.

Never dry your swimsuit in the sun or in a dryer.
The sun and the dryer are both hard on the lycra and spandex in your suit. The sun will speed fading and both will cause the breakdown of the elastic quality of your swimwear.

Alternate swimsuits
Try and give your swimsuits at least 24 hours to dry before reusing. The lycra/spandex is a memory yarn. The swimsuit needs these 24 hrs to go back to its original shape. This will help stop the problem where your suit keeps getting longer.