I did a search to see if anyone has studied people who enjoy "my little pony" porn. Apparently there are many others with your bf's inclination. There are articles out there if you're interested in reading more about it Melen. One researcher suggested that it is most common among male millennials aged 18-24 in a similar way to what they deemed "nostalgic cartoon porn" such as based on shows like 'Family Guy.' It is better explained in the articles than I could summarize here. I didn't include links because I don't want to bother you if you'd rather not read about it. But if you're trying to understand it, there seem to be several articles out there based on research and don't worry, they don't include any pornographic images. They are written by people who wondered why men are drawn to that particular type of porn so they studied it.