Rebecca Simpson died from a head injury after being found at the bottom of the stairs at her home in Castleford.
Ricky Knott with be sentenced today (Friday January 17) after pleading guilty to manslaughter over the death of Rebecca Simpson.
Miss Simpson, 30, died from a serious head injury after being found at the foot of the stairs at her home on Smawthorne Grove, Castleford, on August 26 last year.
Knott, 32, was accused of murder but pleaded guilty to manslaughter yesterday, part way through his trial at Leeds Crown Court.
MORE: Murder trial ends as boyfriend admits killing girlfriend whose body was found at bottom of stairs at her Castleford homeThe prosecution accepted the plea after the court heard Knott accepted pushing Miss Simpson but did not intend to cause her to fall down the stairs.
Knott's barrister, Bryan Cox QC, read a letter to the court which was written by the defendant after he finally admitting responsibility for her death.
The letter read: "I can't put in to word how sorry I am to Rebecca's family, especially her son Braxton.
"It was not my intention for any of this to happen at all.
"I cannot believe an action by me has caused someone to lose their mother, daughter, sister.
"Rebecca was amazing. I will regret what has happened for the rest of my life.
"Not only have I lost my girlfriend but my best friend and there is no one to blame but myself."
Knott, of Arnside Close, Castleford, also stated that he was sorry for not admitting his guilt much earlier.
He wrote: "I could not even admit to myself, let alone anyone else."
Earlier, prosecutor Simon Myerson QC told the court that the manslaughter plea was acceptable to the Crown after consultation with police and Miss Simpson's family.
He said: "Mr Knott now accepts his part in these events.
"The police and the family agree that this is an appropriate course of action.
"The have, by virtue of this plea, the assurance of seeing the man responsible for the death of Rebecca Simpson accept his responsibility for her manslaughter.
"They are not people baying for vengeance.
"They are remarkably self-contained, fair-minded and struggling to do the best that they can with what has happened, without seeking to exert or extract the maximum amount from Mr Knott."
Knott will be sentenced before Mr Justice Jay today.