Sorry, I completed forgot to answer ><"
Looking at the calculus of the Line End, it is quite odd.
It seems that your End is the (PlayerCamera + forward * 5000) but since you want the check to be done from the Slender and not the player, you should use GetActorLocation() instead of GetPlayerCameraManager(0)->GetWorldLocation().
Is it the expected behavior ?
Besides, I believe the PlayerCameraManager may not be always at the camera location. Use GetPlayerCameraManager(0)->GetCameraLocation() instead for futures operations.
PS : Although I am also French, it is better to continue in English, as someone else may help you or is trying to achieve the same thing and might find answer here.