Matthew Sharpe, 40, of Eynesbury, St Neots, killed Andrew Hasler, 28, in the onslaught at his home in St Ives, Cambridgeshire, on 8 January.
He admitted the murder and also pleaded guilty to the attempted murder of his ex-girlfriend Charna Knights, 27.
At Cambridge Crown Court he jailed for life with a minimum of 25 years.
Sharpe was also sentenced to 20 years for the attempted murder of Ms Knights, to be served concurrently.
Mr Hasler had been repeatedly stabbed and died from a single wound to the heart.
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Ms Knights' life was only saved after a neighbour heard a "commotion" and rushed to the house to intervene, Cambridgeshire Police said.
The neighbour found Sharpe on top of her, with Mr Hasler lying wounded nearby.
Police said the unnamed neighbour kicked the knife out of Sharpe's hand and attempted to restrain him, but Sharpe escaped.
Sharpe was apprehended after jumping into the river in St Ives. Police said he was found to have self-inflicted injuries that required hospital treatment.
In a statement released shortly after Mr Hasler's death. his family described him as a "much-loved son, brother, grandson, nephew and friend".
"Kind-hearted and living his life to the full, he came into the world early and has left us far too soon."
The neighbour who saved Ms Knights' life was awarded £1,000 by the High Sheriff.
A man who launched a brutal stabbing attack, killing a man and seriously injuring his ex-girlfriend, has been jailed for 25 years.