Michael Kelly, 46, snapped because he could not deal with the fact his relationship with Sally Cox had come to an end.
The couple had moved into a house in Mold Crescent, Banbury, in Oxfordshire, in February last year but separated in November.
Weeks later, in a fit of rage, Kelly put on a Halloween-style mask before butchering Ms Cox, 43, and her son, 22-year-old Martin Faulkner.
Police called to the end-terrace property last December 13 were faced with a “horrific scene”.
Detectives believe Ms Cox’s daughter Amy, 19 at the time, and another girl, who cannot be named for legal reasons, would also have fallen victim to Kelly had they not managed to escape while the attacks were going on.
Amy jumped from a first-floor bedroom window, suffering serious injuries as a result, after her brother stepped between her and Kelly.
Kelly, of Hatch Road, Swindon, Wiltshire, fled the scene but was arrested by police officers in his home town just hours after the bodies were found.
Yesterday, at Oxford Crown Court Kelly pleaded guilty to two counts of murder and causing grievous bodily harm with intent, Thames Valley Police said.
A judge told him that he will have to serve a minimum of 30 years behind bars before he will be eligible for parole.
In a statement issued through police after the case, relatives of the victims said it was a “sad and meaningless loss”.
They added: “Today has seen justice done for Sally and Martin, although no sentence will ever be long enough for the hurt and suffering that he has put the family through, not least of all the suffering that Sally and Martin went through.”
They went on: “The family would also like to thank Thames Valley Police for their help and support through this sad and meaningless loss.”
Detective Chief Inspector Peter Vigurs, of Thames Valley Police, said: “Kelly has pleaded guilty today and I welcome the sentences handed down.
“Our sympathies go to the family and I very much hope that what has happened here today may, in some small way, allow them to begin the next stage of their lives.”