Diaper fetishists are adults who wear diapers for non-medical reasons. These could include convenience, sexual pleasure, or simply preferring the way they feel wearing them over underwear. This page explains the basics of what a DL (Diaper Lover, in English) is and how to understand where that fetishism comes from.
Steps
Step 1. Approach the topic with an open mind
See how to open your mind.
Step 2. Realize that many DLs have previously had problems with incontinence (uncontrolled accidents)
As a result, they had to wear diapers and, over time, they ended up liking some of their aspects.
Step 3. Understand that while some people like diapers for sexual reasons, it is only to be expected
People sexually enjoy many types of objects, ranging from leather and rubber, to more complicated things, such as wearing clothes of the opposite sex. Since diapers are soft, sometimes warm, and positioned right on the sexual organs, it would be surprising if they didn't trigger sexual urges, at least in some people.
Step 4. Know that diaper fetishists are not pedophiles
Reputable psychologists have noted and confirmed that there are no such connections. This is known in the community, to the point of being clearly stated on Wikipedia, but sometimes uninformed people still make connections that don't exist.
Step 5. Check out some educational sites like Wikipedia
Step 6. Ask a diaper fetishist to explain the situation to you
However, keep in mind that he may be reluctant to do so, unless he trusts you a lot.