Hi fishingbee

Try your mates rod /line and see if it still lands in 's' shapes ......if so then the problem is yours....the fly line will only 'track' the path that the rod tip goes.
This is a technique that you may find useful in a more advanced stage as you can build in 'kicks' in the line to avoid obstacles or current shifts.(don't worry about that now....you need to cure your fault first)....answer ...get casting lessons
The other option is that it is the line that has developed a memory of the coiled position whilst on the reel.....and this is the option relating to if when using your mates rod it lands straight.....answer... get a new line