What if I told you that I'm actively avoiding my best friend?
Oh so this is happening for real now or what? Why are you avoiding your best friend?
When he told me he found a girlfriend, I was not happy with him.
It's not good for you to be so possessive about your friends. You call him your best friend so it's not right to avoid him. It will hurt him.
Pfft, he ignored me for 6 months so it's his fault.
Ignoring your best friend over him dating someone is somewhat possessive or maybe even more than that. I feel you need to find a significant other yourself and only spend time with them now. Otherwise talk to him to explain how you feel without avoiding him, revenge is never sweet.