Cornelius Brown, 23, of Greenhill Lane, Riddings pleaded guilty to stabbing Jade Riley-Ward in Somercotes, Derbyshire earlier this year.
Ms Riley-Ward, 30, suffered more than 80 stab wounds in the attack at her home in September 2012, which the judge described as "torture".
Judge Jonathan Teare described Brown as "intensely jealous" and "possessive". He will serve a minimum of 20 years.
At Nottingham Crown Court, Judge Teare told Brown: "You were intensely jealous and intensely possessive of her.
"She was defenceless. Your attack on Jade was vicious and prolonged and it would not be wrong to describe it as torture.
"The whole family is devastated by her pointless death at such a young age when she had so much to look forward to."
The court heard Ms Riley-Ward had been Brown's babysitter when he was younger and they had been in a relationship for eight months.
Judge Teare said Brown had "convinced himself" that she was having an affair. He attacked her with four kitchen knives.
Speaking after the sentencing, Det Ch Insp Karen Pearson from the East Midlands Specialist Operations Unit, said: "The last 14 months has been horrendous for the family.
"Their whole world has fallen apart.
"Today's sentence won't bring Jade back but they can now continue in their recovery from the grief knowing he [Brown] has got the justice he deserves."
A man who admitted the murder of his ex-girlfriend has been jailed for life.