My girl dosent wanna give me her fb password,like she did before?

when we started talking,she gave me her fb password,and she trusted me,so i saw a few things,and approached her,but i assumed wrong,so about 4 moths later,i asked her for her password again,and she told me,shes not gonna give it to me,because if i really love her,and trust her,i wouldnt be asking to see if shes messing with someone else.so i gave her my fb passwrd,and she told me twice,that she dosent want it,she told me,she wanna go on with us having trust,she wants me to buid a trust and love like we havnet before.but...in the 2nd months,shes been kinda laggy and laid back,and i seee her on fb chtting a lot,without me there,she hasnt sent me pictures sense the 2nd months,she use to text me everyday,and use to be always talking to me,but everytime,i tell her,about it,she gets mad,and says,i love you,but this is getting old,if u dont trust me,lets just shut it down cause we are not getting far. but what do u people think. cause idk what to do,she wnt give it to me now,like she did before