Are both sentences OK?
Finally, I've found someone who appreciates me.
Now I've found out who you are. (I mean you're not good person)

Question

Answer

Finally, I've found someone who appreciates me. (Perfect!)
I finally see who you really are. (we say this more often)

OR!

Now I see who you really are.
Your true colours have come shining through (not often said, but sounds good and plays on a classic english saying)

Answer

I’ve finally found someone who appreciates me.
Now that I found out who you are.  (I mean you’re not a good person).