The actress, whose character Ronnie Branning was at the centre of the show's controversial baby swap storyline, has been unhappy for some time but was persuaded to stay by producers, the Daily Star Sunday reports.
A source said: "Sam has been thinking about leaving since 2008. There seemed to be a few teething problems early on and things appeared difficult with one fellow actor. But all that blew over before it all kicked off again over her on-screen daughter Danielle's death in 2009.
"She had a particularly difficult time of it last year when she had to film her on-screen dad's murder as she was coming to terms with losing her dad in real life. She found it all incredibly hard and it really took its toll on her emotionally. But show bosses managed to persuade her to stay, although she still wasn't completely happy.
"Barbara Windsor leaving last year was another blow and she's really missed having her around on set. The baby swap storyline was always going to signal the end of her time on the show but it was up to her how long it would last. It all came to a head last week when she'd decided she'd just had enough."
It was recently confirmed that Womack will leave EastEnders after nearly four years when the current storyline comes to an end.