The first person was someone on Beastforum and we ended up meeting up, just once, at a big animal convention thing. I wouldn't say that counts.
The first real person I told was the first woman I ever fell in love with. On our first date kinda, she told me everything about the weed she was growing industrially and all kinds, she entrusted a lot of information with me. So when the time came I was almost certain she would take it well. Do note I was 29 and her, 40.
We were lying in bed one night, only a few weeks after getting together and she asked me what I really wanted to do in my life, what do I chase? And I answered, hesitatingly, that I wanted to have sex... with a dolphin. Oh she said. I said no more and she was quiet for like 2 minutes processing this information. She's never even thought of this as a thing before. Then she obviously asked about why and my background with animals and such. I told her everything about how I came to be zoo and what I love about animals. I said I had proof and grabbed my phone, showed her me fucking a horse and then proceeded to actually watch, in full, the other animal porn I had saved on there. She was not turned on by any of it, but her open mind accepted it without judgment and she was very curious about this new flavor of canned worms.
I love her dearly still, but it never lasted more than 3 months. It wasn't because of anything I mentioned above, it was because of our difference in experience when it comes to love and relationships.
And then I told a second person about it as well, she was a friend in the same place and kind of interviewing me. She writes books and things and likes to figure out how people think and function. She wasn't appalled either, and was questioning why I would tell her that. I thought she was trustworthy and open minded is what I said to her. To be fair, I do have an extremely good record of being able to judge people after only a couple of minutes talking with them, it must be a hidden talent.