Graham Sneddon,32, sent a series of threatening text messages to the women after a friendship that he had with one of them turned sour.
The High Court in Edinburgh heard that one message read: “Let’s see how long you have your kids after tomorrow.”
He sent another message in which he detailed the objects in one of the woman’s home - although the mum had no knowledge of the sex offender ever visiting her.
Now, Sneddon faces the prospect of having to spend the rest of his life behind bars.
On Monday, judge Lord Pentland handed him an Order for Lifelong Restriction at the High Court. This means Sneddon can only be released from jail when the parole board consider him not to be a threat to public safety.
Telling him that he would have to serve at least 18 months in prison, Lord Pentland added: “Having considered all of the evidence, I am satisfied that you present a high risk to public safety.
“The punishment part of your sentence will be 18 months. I must emphasise to you that you will not be released at the end of that sentence.
“You will only be released from custody once the parole board consider that you no longer present a risk to the public.”
Sneddon, of Arnot Street, Falkirk, had originally appeared at the town’s sheriff court to admit two charges of sending text messages which contained threats of violence and a charge of struggling with the police on July 6 2012.
He was caged in 1998 for raping a 14-year-old boy. He also abused two girls after his 2002 release.
Sheriff John Mundy sent the case to the High Court in Edinburgh in August 2013 saying he thought the maximum sentence that he could impose would be too light.
During proceedings, the court heard how Sneddon and one of the mums, who was living in the Melton Mowbray area in England, had been contacting each other for a couple of years using Facebook.
She thought they were “just friends” and told him to stop calling her “babe” and saying that he loved her.
When she deleted him from Facebook in May 2012, she began to find as many as 40 missed calls on her phone and threats that Sneddon would “smash her partner’s face in”.
Her friend also became involved after she took the phone during one conversation and told Sneddon to calm down.
She received a text telling her: “Kiss your kids good night... it maybe the last time you see them.”
Around this time she found that she had 237 texts from Sneddon’s phone. Some merely said ‘boo’ but others were more menacing. One described the various items in her home.
The other mum - Sneddon’s former Facebook friend - was told “Let’s see how long you have your kids after tomorrow.”
Sneddon kept saying that he was travelling to Melton Mowbray.
Sheriff Mundy was told that both women left their homes and reported Sneddon to police in Leicestershire.
Police raided Sneddon’s Falkirk home and found items linking him to his Facebook friend, including a Valentine’s Card but denied that he was behind the threatening messages.
While being interviewed in Falkirk police station, he threatened to stab one officer in the eye with a pen and had to be restrained.
The local authority reacted to news that Sneddon had landed a job in McDonald’s by obtaining a Sexual Offences Prevention Order.
Sneddon admitted that he had breached the order twice in minor ways - once by travelling too far from his home and once by shouting to girls from the balcony of his home.
Now, he faces the prospect of having to spend the rest of his life behind bars.