Asher Maslin, who brutally killed his ex-girlfriend Hollie Gazzard when she dumped him, "couldn't take rejection," police said.
Detective Inspector Angela Middlewood, of Gloucestershire Police, said: "He was a very volatile individual. He was very controlling and possessive.
"Hollie had broken off the relationship with Maslin and he couldn't take the rejection."
She added: "I don't think we believe that Hollie thought that something as brutal and awful as that would happen but she was aware that he would turn up and pester her and couldn't accept that the relationship was over."
More top news
Ed Miliband will order an emergency recruitment drive of nurses so an extra 20,000 will be working in the NHS by 2020.
Sir John will give a speech later today saying a Labour-SNP government would be "weak and unstable" and wreck Britain's economic recovery.
Nigel Farage has told ITV News he would "happily" accept Christian refugees into Britain because they have "literally got nowhere to go".