Steven Williams, 31, went berserk with a kitchen knife following an argument with new girlfriend Joanna Hall at her flat in Tenby, west Wales, last year.
The alcoholic growled at the 35-year-old "will you just die" - before leaving her to suffer as she bled from several deep slash and stab wounds.
When he eventually did call paramedics, Williams claimed a mad-man must have broken into the flat while he had popped out to buy booze.
But Ms Hall was able to describe the attack from her hospital bed.
She died three weeks later from her injuries.
Despite the damning evidence against him, deluded Williams continued to stick to his story throughout his trial at Swansea Crown Court - where a jury eventually convicted him of murder.
Sentencing Williams to life in prison, Judge Mrs Justice Nicola Davies described him as "brutal" and "callous" but "not sadistic".
She said: "You did not take a knife to Joanna's flat and you did not go there intending to murder her.
"Joanna was an emotionally vulnerable woman who was physically smaller than you.
"This was a sustained and brutal attack using a knife on a defenceless victim.
"You stabbed her more than 20 times on occasion penetrating organs within her body.
"You denied the Joanna the medical attention that she so urgently needed.
"In doing so, you were cruelly and callously indifferent to her condition."