why he isnt telling me that he talks to "her"?

[Abigail]

One day just stop messaging him on the fake account, don't ever bring it up or tell him it was you.
Put yourself in his situation:
Your boyfriend makes a fake account on Facebook (you think it's some random guy) you end up telling him stuff you don't think you should have and the next day you find out it was him. Personally I would be mad if my boyfriend did that to me, I would feel as if he had no trust in me.

I know this was probably not the answer you were looking for, but this is my two sense on this problem