A HEARTBROKEN woman stabbed her cheating boyfriend to death when he shattered her dreams of love and marriage, a court heard yesterday. Promsuwan Sirilak, 41, left Thailand for a new life in Hong Kong, where she fell for the charms of Cheng Wing-tong, 38, the High Court was told. She moved in with him and he promised to marry her. But her hopes were destroyed when he began beating her and started dating a younger woman. The final straw came when he tricked Sirilak into leaving the home they had shared so he could take his new girlfriend there. When she discovered the truth, Sirilak confronted him on the doorstep and thrust a knife into him. Mr Justice Seagroatt said: 'I am satisfied that she became the abused companion of a man who probably wanted to maintain two relationships, if both parties were available, and certainly was unfaithful to her. 'Such behaviour on his part can never justify the taking of life but, in a highly volatile emotional situation, tragedies often result.' Sirilak, a helper in a home for the elderly, admitted manslaughter. Her denial of murder on the grounds of diminished responsibility was accepted. Neville Sarony, QC, defending, said: 'This lady is perhaps more sinned against than sinning.' He said she had met Cheng in a Wan Chai bar in April 1993 and fallen in love. But the romance soon turned sour. By June, she knew he was having an affair. Cheng told her he was seeing Olivia Taepo, 36, 'just for fun' and continued to declare his intention to marry her. On April 28 last year, Cheng told Sirilak she would have to leave the flat they shared in Kwai Chung because his parents, who usually lived there, were returning from a holiday. In fact, he just wanted her out of the way so he could take his girlfriend there, the court heard. When Sirilak confronted him, he told her their affair was over. 'One needs very little imagination to begin to understand the emotions that must have gone through this lady's mind at that time,' said Mr Sarony. The prosecutor, Barry Moorfoot, said Sirilak had smashed a window and later returned with a knife. Cheng went into the corridor to speak to her and, 15 minutes later, Miss Taepo heard him screaming in pain and shouting for help. He died from the stab wound. Sirilak fled the scene but later gave herself up to the police. The court heard she was suffering from a severe depressive illness aggravated by a thyroid disorder. The judge ordered she be treated in Siu Lam psychiatric centre for three years.