Prevent trouser damage when biking? I am biking nearly every day to work and back (~ 3 km), but my trousers get damaged quite fast due to the created friction between my legs and the saddle. Which then means that I have to buy new ones rather frequently. Is there any way to prevent that?

Saddle in question:
Jeans and similar trousers wear fast on saddles. This is partly the seam on the inside of the leg, which is more of an issue on thick, high-friction fabric. They're also not very comfortable for riding in, especially if they get wet (including from sweat). Sitting in wet clothes when you arrive isn't much fun either, and smart stuff doesn't like being rained on.

My solution on commutes over about 8 km (5 miles) is to get changed. This also means I don't get chain oil on anything that matters. I'm not suggesting lycra as a default for commuting; apart from anything else pockets are useful at the ends. Gym shorts are good in summer, but in winter I suggest quick drying hiking trousers, and cheap ones at that. The pair I relegated to bike commuting have done a few thousand miles/km without noticeable wear.