Why do i lie so much?

i am a big lier, i have always had this problem even as a young girl. i always got BEATINGS for this i figured i would grow out of it but i havent. now that i am 21 i still lie. its hurting my relationship w/ my fiance'. we have three kids together and i love him so much but for come strange reason i cant let my past go. example: my first time was w/ a guy name E (ive only been with him and my fiance') it seems i cnt stop thinking about him. first of all troy(fiance) met me whn i was 16 but i lied about my age he was 22 at the time and i was also still dating E evenually i broke it off with E b/c i felt like troy is what i needed in my life. E moved on and i moved on but eventually we will always bump right back into each other and troy finds out everytime, well for the past 4yrs i found out troy has been Cheating on me w/ all sorts of women, so i hooked up w/ E again b/c i was upset and i ended up pregnant but i knew E wasnt the daddy i knew it was troys but i lied and i told E its his and troy still think the bby is his, now i got myself in a big situation...... me and troy trying to start ova and make our realationship work but E keep popping up just making the situation worse i dnt want to tell E the truth b/c i care about him but thn again i love troy and i want to spend the rest of my life with him ...................i promised myself a month ago that i was through with lying to myself and everyone else b/c im hurting me and others and i feel like i have no reasin to lie to anyone about anything ....i really want to get some kind of counseling b/c i honestly think i have a problem BASICALLY MY QUESTION IS DO U THINK LYING IS A SICKNESS?