This guy and I were dating before he got with this girl and he lied to me so he can be with her. How can I put a curse on someone so him and his girlfriend will break up.

Merry Meet Seeker,
It is sad to hear that your boyfriend is dating someone else. These things happen and you will feel sad or angry but it is not a good thing to put a curse on anyone because they hurt you.
Do you know what will happen if you put a curse on anyone? First of all, the Universe will be very very upset that you purposely hurt or planned to hurt someone else, especially someone whom you love or loved before. Putting a curse on anyone will immediately cause us to lose something in our life as a backlash from the Universe. Anytime we hurt another, we will hear from the Universe. At times, we may not “hear” that well because we are so preoccupied with our life that we forget when we hurt another.
Only when we get the brunt of the hurt will we remember that we may have done something wrong to somebody else. Yeah, the Universe does not discriminate. For example, if a person got angry with someone and kicked a dog on the way, the dog may not bite you, but someone, down the road may hurt you in some way. See the connection? Only when we understand the connection between our behaviour and our experieces in the following days or months, will be connect this experience to the karma we have generated by kicking the dog.
Many people complain about sorrowful circumstances without thinking of why this is happening in our life. We only remember the good things we have done even if it was years ago. Most of us forget the negative things we have said or done angrily to our parents, sisters, brothers, friends, strangers, animals, etc
When we are aware of the karma we collect for doing good or bad deeds will we understand how the Universe works.
Brightest Blessings
Rose.