This is actually perfectly normal based on the psychological definition of "fetish" a fetish is when sexual stimulation and orgasm can only be achieved by having an inanimate object nearby that helps with the process. In this case, Diapers. I would recommend trying to imagine yourself sexually with a female, not involving diapers, and trying to find a way that it sexually excites you without your fetish. This is the way it is done in fetish clinics acros the country, and once the correct motivator is found there shouldn't be a problem. If this type of "self-therapy" does not help, Perhaps during the sexual act, use your imagination to insert some ABDL things without her knowledge.
I hope that this helps.
-Has a masters in psychology, is in the process of a PHD.