How do you tell your girlfriend you think you’re fictionkin if all they’ve done when you’ve mentioned kin things is shun you.

Find a girlfriend who doesn’t abuse you by shutting you down when you talk about your interests. 

Seriouisly, kin stuff or not, a significant other should express interest in the things you’re interested in, even if they think they’re silly or weird. 

If someone is ‘shunning’ you for something you have interest in, you aren’t they problem, and you don’t need to cater to them. They are the problem and you need to either confront them with their shitty behavior or drop them like a hot potato.