Should I trust my partner

Hi I recently got back with my ex partner. I went threw his Facebook and I see a message from a women  saying do u you still like my friend and would like to get closer to her. He put ok . He admitted that he wanted to fuck her  while we wasn't together . I have asked him to block both of these women on socail media and he has. But he still feels the need to talk to them if he see's them I don't like it. I Know I shouldn't of gone threw his Facebook and was wronge.