He was going to propose her in front of everyone.she told him that he has to propose her well to accept him.he proposed her in front of everyone it was a planned drama..but in front of everyone she said that she doesn't love him but loves his sister's boy friend.she was threatened to do so.she could have told him the reason as they both were alone.he used to trust her n asked him why she did that.but she was rude in her reply.but as you said he had no right to kill her n it was completely wrong.but as you said that day itself they showed that he was not in his control. even before that night priya's mom locked her in the room.because she knew that the ML won't be in his senses that night.last week he tried to remember what happened after theor encounter n he couldn't recal anything.so I think as you said they were trying to make us believe that he was not in his senses when he tried to kill her.otherwise why would he forget it?they can show any illogical thing in supernatural shows.hypnotism is there in every supernatural show to justify the lead's stupid actions I think.
What did she hide or cheated? Still no matter what she does or hides does not justifies him killing or trying to kill her except for self-defence. Like in Prithvi Vallabh if FL tried to uncessarily hurt ML then killing her as self-defence was okay. Same goes for Priya who can't harm anyone without reason. They better show someone hypnotizing him to kill her like it happened in Ekta's Chandrakanta.
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