you are being a supportive Girlfriend and letting him express himself encouragment is also good, as long as you and him dont have any problems with it I think it should be fine
on a related note : I had almost the same conversation with my Girlfriend when I told her that I liked diapers, my gf encourages me to wear them as well, she put a diaper on me one time ( I had hurt my toe and couldnt walk on my foot ) I was content , I had asked her to change me once she told me no for good reason ( she is a CNA and changes her clients for a living ) but all and all keep being supportive and everything should be fine