I'm going to refuse to share details of my life with my best friend
Why do you not want to share with him?
I was curious so I checked his social media, he's been flirting with other guys and that hurts my feelings (emotional reasoning and lack of empathy and violation of privacy)
You should be honest with your friends. If you are jealous you should tell him and see if he likes you back.
Gonna use this to manipulate him into dating me.
That's wrong. You need to be hones with him, not manipulative. You risk destroying your relationship with him otherwise.