Ok I am really mad and I need answers?

If you left someone whom u were with for almost 5 years...first off could u fall out of love with them , move on , be in love with someone else, and be truly happy in a couple months after leaving the 5 year relationship??? Even also, telling the one whom u left, loving and positive things about u two for the first two months after leaving them??? And secondly, ur the one who left and ur new girlfriend was sending stuff to your ex ( like emails for invitations to a call site and game site and to join facebook), wouldnt u think that is sick and morbid when things werent mutual and ended bad???? (oh yeah and the one whom left, please picture this as you, you have bipolar)