How do you let go of the one person you really loved?

my bf dumped me 3weeks ago we always sed we were soulmates we had some really bad times and he was very controling he made me think he was the best thing i could ever get and after 3weeks he happy and forgot about me so it seems we were together nearly3years he been a dad to my son and now has gone he dump me for night out wiv his friends he 31 and am 22 then i found out he had been datein a girl while he was wiv me for a fuw months i feel really ill inside i realy hate him but everytime i see him it hurts we work in the same office al i want to do is hurt him and let every1no about his lies and what kind person he really is i just want the man out my head i dnt wnt him back and i no we were wrong but how do i get al the goodtimes out my head cos thats al i can rem i dnt think ov al the bad stuf he put me thro i put on a brave face but really al i wnt to do is cry i even had his name i had tatto on my leg covered over.he cant even look me in the eye at work my heart is really hurtin