It's tough. Isn't it? You feel this tremendous emotional connection to one person... Loving him or her like you never thought you were able to love. The problem? You're married to someone else.
Though limerence by its very nature is relatively short-lived (typically lasting somewhere between 3 months and 36 months) it is a very real and intense emotion/feeling. When a person decides to leave a limerent relationship, or if they are the one abandoned by the other, the emotions don't immediately disappear.