Stuart Thomas stabbed hairdresser Katrina O'Hara twice in the chest with a large kitchen knife at her salon in Blandford Forum, Dorset, on 7 January.
The jury had heard Thomas, 49, had been arrested days before for harassing Ms O'Hara, 44.
He was convicted of murder and jailed for life with a minimum of 26 years.
A married father who was under a restraining order for harassing another woman when he killed his estranged lover has been jailed.