Exes & fiancé

My fiancés ex girlfriend still has him on Facebook. He posted and said "at (restaraunt name) with family".) His ex girlfriend comments and says "oh I just left my shift there. Wish I could have been there to seat you!" I have a feeling he posted it just to let her know he was there. So I told him that I didn't want him talking to her. He goes & blocks her and tells me he did. So I said ok that's fine. I didn't even tell him to. Later, I figure out that he unblocked her & added her back.  I just let it go & didn't say anything...