You really bared part of your soul for us today; that's really awesome
The first thing I want to touch on might seem obvious but I feel like it still needs to be said: you have absolutely no reason to feel guilty. I know that it's not going to change how you feel, and your feelings are 100% valid, you need to accept them for what they are and also understand that you've done nothing wrong.
I've also been with the show since the first episode in 2011; I've been a fan of ponies since I was a kid and it was cool to see a reboot with an art style that was, in my opinion, significantly cuter than previous generations on top of having Lauren Faust of all people be a part of it! That, and Tara Strong, got me interested I was lucky to have that available to me as it sounds like you have been suppressed and stunted. I have a lot of childhood trauma that has given me the same kind of "Peter Pan Syndrome" (my therapist agrees with that term lol) which is connected with a lot of my mental health problems and one thing that really, really helped me is hearing my therapist tell me that not only is there absolutely nothing wrong with enjoying and participating in childish behaviour but it's actually good for you. It's normal, and if it makes you happy then there's nothing wrong with it. You're not hurting anyone nor yourself. I learned how to get over myself, my fears, and learned to simply embrace that part of me. Yes, I play with toys. I mean, I don't exactly sit on the floor everyday and fwoom, zoom, kaboom little plastic horses around but I do sit at a table and, internally, create scenes and dialogue and I will move them around. I literally have a small set-up where I play with toys on occasion I'm going to be 28 this year.
Just as well, while the fandom is sort of shrinking a little, I don't see what everyone else is seeing in regards to the fandom eventually caving in completely when even a group of 100 people can make up a fandom. Joining late in the game, to me, is proof that the show really still holds up and will captivate new and old fans for a while. I actually disappeared from the fandom for a while before getting back into it because I started to miss having people to discuss colourful horses with. I want to make friends, connections, and extend them beyond the fandom. Sharing a single common interest is great, but the best thing is making a friend who sticks with you through and through Ponies or not. Besides, there are still loads of people making art, music, projects, the works! Certainly not as much as the old glory days, but I'm actually working on a comic set in that universe (just for fun, nothing super serious lol).
If the fandom one day disappears to the point where even this site is taken down, I would HOPE that all of my friends have me on Discord, Facebook, etc so we can still be just that.
Ponies brought us together but they are not the glue that binds us I've re-watched all of it twice, in order, in the last two months because I love this show so much. When it ends, I'll re-watch it again, and again, and again
And if you ever need someone to talk to privately, my inbox is always open! (I feel we might share similar traumas... I've been in a couple of severely abusive relationships as well.)