Yes, the rain will ruin your suede jacket. Suede is a porous material, and that is why it is very easily marked by water and that is why you should avoid wearing a suede jacket in rainy conditions. Although the watermarks can be removed to restore the jacket to its original condition, if your jacket gets drenched, it will wash out all the natural oils leaving the jacket shiny and stiff. So, to stay safe, just avoid the rain.