Is my boyfriend hiding something from me

Britney
I was just scrolling through Facebook and I saw that my boyfriend had added this girl and I was so mad because he doesn't want me talking to guys etc, so I was fuming that he would do that to me, then I asked him about it and he is saying that Facebook added her he has never seen her before in his life, he has never talked to her etc. what should I do, should I believe him. He has never done anything like this before and then when I confronted him about it he just ignored me. Which just made me more mad. Am I overreacting about this whole thing?
UPDATE
Okay so I told him to delete her and he didn't have a problem with it but then after it all he started ignoring me again. So I brought his mom into it and asked her why he would do that and she was showing me there conversations between them in texting and he was saying stuff like make sure she's okay and some other bs like why don't you make sure I'm freaking okay and not your mom.