I'm talking to my boyfriend's best friend on a fake tinder account and we're falling for each other...
Oh my I cannot believe what you are telling me! Why did you start talking to your boyfriend's best friend on a fake tinder account?
I was so insecure in my relationship and wanted to know if he had cheated on me.
Being insecure shouldn't cause you to commit infidelity, though. Aside from that, it's your boyfriends best friend. You're not afraid he'll say something?
He never told anyone and I feel fine. I won't stop talking to him.
It sounds like you're not happy in your current relationship. So my advice would be to either talk to your boyfriend or break up, as cheating is never the answer.