First i would like to say I have been a Christian since i was eight and have study the Bible since i have 3 degrees in bible B.A, Associates, Minor, then i will leave my denomination and bible school name out of this.
One God made sex to be enjoyed between husband and wife
the bible states
Hebrews 13:4 Marriage is honourable in all, and the bed undefiled
Titus 1:15 Unto the pure all things are pure:
wearing diapers for pleaser or fun is not a sin against or any one else for that mater
there are no indications i the bible that sexual fetishes are sin or that there not just that we work things out between us and God
what a person does is between them and God and what happens in the bedroom or in the private
I believe the angels and God turn their backs to give us privacy to have a little bit of fun and pleasure when we are with our mates
I think that what ever we wear we must remember that God look on the inside at our hearts not th out side 1st Samuel 16:7
by the way i do not believe it is a sin