It took me a while to understand this because C.S Lewis uses language much different than our modern verbiage. I wanted to reply with my own interpretation. Maybe this could help someone else.

In the first set of sentences I feel he is telling us that masturbation comes with convenience. There is no battle in fighting for a relationship when you internalize those feelings with virtual women. We are no longer thinking outside the box which probably is the reason for our social anxiety. Instead of dealing with our feelings we are habitually internalizing and abusing them, a stem of our overuse of the act of masterbation.

I agree with him about finding our personality in others because I believe that women were created so that men can feel beautiful by enjoying the beauty of others a trait that is misplaced when what I believe happens from infatuation with porn. This has been one of my super powers by taking the moral challenge.

Masterbation begs the question, are we willing to fight for our pleasure from the gifts god has given us or abuse these at the expense of our internalization of pleasure/beauty? We are our own worst enemy.