Why do you think she changed and how to I change her back??

my girlfrd and I are in a long distant relationship. and we’ve been 2gether for over a year now.. at the beginning we love each other soo much.. but since we’re far away. I controlled her and im regertting it now.. she changed.. she said but its like just over these few days.. she changed like shes like she dotn care anymore.. like she dont want to talk to me anymore.. and 3 days ago.. she blocked me.. she said it was a mistake.. but I think its impossible.. though my frds asked me to trust her.. its not that I dont trust her.. im just worried… and I got doubts… and just now.. she said shes tired and said shes gonan go sleep.. and then went offline.. but she blocked me actually.. she was online in my frds account.. I asked her why she blocked me and she said she didnt and yet she was online.. but offline in my acc.. then she just denied and denied and denied. she said shes just testing if I trust her or not.. and after that.. she kept on dening again.. saying she wasnt online.. whts going on?? why do you think she changed??? why did she blcok me?? sehs being unfaithful… thts wht I tink.. wht do I do???