I don't know what to do, plz help me out!?

your mom gave you good advice. what she did was a sign of a bad character and most likely the person she cheated on you with dumped her and she doesn't want to be alone so she came calling to you again because she knows you love her. if you do give her another chance because your heart won't allow otherwise then be smarter this time and expect the worse and hope for the best. just be prepared heart wise either way.