Should I ask to see his phone?

At the beginning of our relationship I had a gut feeling that my bf was talking and flirting with other people. Turns out I was right. Also I found out he was best friends with this bitch that was my worst enemy and was the meanest bitch alive. I asked him to unfollow her since she bullied the shit out of me. He said ok.

Lately I’ve been getting the same feeling about him doing things behind my back. I want to ask to see his Facebook and I just need to know and see for myself if he still follows that bitch and if he’s doing things behind my back again. How should I do this? I want to stay with him but I’m nervous and scared of what I’ll find and the big argument that will ensue.