It used to be totally sexual, but as I began to wear diapers more (24/7 for 3+ yrs), it has definitely shifted towards being more mentally aroused, (with sexual moments - can't keep wood forever...), and more of a "wearing for need", whether psychological, or physical (comfort, convenience, etc.).
I don't think it's necessary to have it all figured out. Just go with the flow. It adjusts itself, as the need arises, probably based on whether you're single, in relationship, or married.
The diapers are me. I don't deny it. I've lost the guilt & shame, and I am just a more balanced person for my wearing.