It actually turns out that Kamal and Rosie loved each other. Rosie just pretended to love me to get the money I had. When Rosie realised that I was going to propose her with a very expensive ring, she thought that it would be enough for Kamal and her to settle down peacefully.
Rosie decided to accept my propsal, get the ring and then breakup with me. But, Kamal feared that I may ask her to return the ring after breakup and ,hence, planned differently. He decided to steal the ring before I propose her, and then Rosie would breakup with me after some time. So, they decided to get rid of me and steal the ring. Kamal knew a goon and asked him to kill me in the restaurant, but, the goon asked for a high price which Kamal couldn't pay. Rosie knew about Theeran and they all teamed up together.
Theeran payed the goon but when he knew that I had a expensive ring, he payed him a bit extra asked the goon to give the ring to him. When Kamal knew about this he got very angry and scolded Rosie due to frustration. This was the reason why she was crying when I woke up in the hospital. Kamal met with the goon and threatened him that he would no longer vouch for him and would have him arrested. Scared, the goon came to Theeran's house to convince him to give the ring back to Kamal. But, Theeran refused which made the goon angry and he left the house. The mysterious guy I saw at Theeran's house was this goon.
Kamal panicked when he realised that I have learnt about the goon and, hence, he came up with his own plan. He told me to hire a detective, killed her and framed Theeran for her death resulting in manhunt for Theeran by the police. Theeran went into hideout, contacted the goon and convinced him to kill Kamal in order to take revenge. The goon too believed that killing Kamal would end his misery and, hence, killed him. An infuriated Rosie thought me to be the reason behind Kamal's death and stabbed me to death. She took the money which I had borrowed from Theeran and left the city.