It's a totally valid thing to do. Don't worry! I have friends that do it too. If you're happy then that's all that matters.
So yes, this is something i hated for years. And now here i am, doing it myself. So i started playing the Harry Potter game hogwarts mystery some time ago and it didn´t took long for me to turn my character, Eris White, into a full on OC because i just grew so attached to her. And while playing, i began shipping her and Tonks. It´s not really a problem with canon because their relationship takes place during their time at hogwarts and thus doesn´t interfere with Tonks and Remus, but it´s still weird to find myself doing something i always considered the number one sin of any fandom, lol.
Honestly you're always going to find a lot of people very against it. And I think part of the reason that you find so many people who are quite so heavily against it is because of fandoms and shipping...when we're not talking about 'well I'm just disinterested in reading a fic about your oc' it's honestly 'you're getting in the way of my ship' type stuff, it feels like.
Honestly do what you like. It's perfectly fine and you can always multi-ship characters anyway!
Also most fandoms are kinda toxic :C