Thanks for query,
First of all remember that sex is in our mind & not in organ.
due to musculature the resting penis & erected penis shows curved position.This is a normal anatomical position so nothing to worry about it's curve.
doesn't affect your penis structure.
The visible is vein not nerves.When you get excited there is a more flow in your penis makes it visible.
This has no relation to nervous system so you have not loss anything.
Try to decrease the frequency of masturbation by yoga
or diverting your mind to other activity.
So nothing to worry.you have no disease.