When they began dating, they agreed to keep the relationship "non-exclusive". But it ended in tragedy after the 28-year-old man realised he could not accept how she had been seeing other men.
During a quarrel outside his Boon Lay flat on Nov 26, 2015, Neo Chun Zheng stabbed Ms Soh Yuan Lin once in the neck with a folding knife, killing the 23-year-old.
Yesterday, Neo, who had initially been charged with murder, pleaded guilty to culpable homicide - and now faces life imprisonment or up to 20 years' jail, with caning.
In April 2014, Neo and Ms Soh, a former air stewardess, started work at the Marina Bay Sands casino as customer relations executives.
Five months later, they began dating. But Ms Soh wanted the relationship to be "open", and to be kept a secret. That did not stop Neo from feeling that he had been cheated whenever he found out she was seeing someone else.
In March 2015, he found out she had been intimate with one of their colleagues. He got hold of compromising photos of her and the colleague, and showed them to other co-workers.
In September that year, they quarrelled after he found out she was texting someone she had kissed at a club. Ms Soh broke up with Neo later that month as she felt he was too possessive. She told him she wanted to remain single.
Neo however found out that she was using the dating app Tinder. He became angry that she had gone back on her promise about staying single. He told a friend he thought about disfiguring her with acid.
Throughout this time, Neo continued telling Ms Soh how much she had hurt him, and that she has to make it up to him by buying meals for him or going out with him.
On Nov 25, 2015, he asked her to watch a movie with him but she replied that she had already seen it with someone she met on Tinder.
He then continued to text and call her until she relented the next evening and bought dinner for him.
Ms Soh went to Neo's Boon Lay Drive flat to deliver a packet of food, but they began quarrelling along the common corridor.
Neo's 62-year-old mother, Madam Ng Lian Kee, came out of the flat and told him to let her leave.
But Neo snatched away Ms Soh's mobile phone and hid it inside the flat. He also took a folding knife from his room, hid it behind his back and asked his mother if she knew how many men Ms Soh had slept with.
Madam Ng saw the knife and tried to wrestle it away. But Neo pushed his mother to the floor and swung the knife at Ms Soh, stabbing her once in the neck.
Neo threw the knife down the rubbish chute and tried to stop the flow of blood from Ms Soh's neck. He gave himself up when the police arrived.
Ms Soh was taken to hospital but was pronounced dead three hours later. The knife was later recovered.
Sentencing has been adjourned after Neo's lawyer R. Thrumurgan disputed the opinion of an Institute of Mental Health psychiatrist that Neo was not suffering from any mental disorder at the time of the stabbing.