Well, honestly I can understand pretty well your desire of revenge, I would never be able to move on if I don’t first make the mf pay.
So here, coincidentally or not there’s this recently topic.
If you identify yourself as a woman I would tell you to call a goddess, Hera maybe, cause they usually are quite interested in cheated woman.
If you don’t, that’s not a problem at all. Any entity would be good to help anyway.
Work with gods are far easier than work with demons in my opinion, I believe any beginner can do it.
So get an offering for the god of your choice, the offering can be anything, a glass of wine, grapes, flowers, a piece of cake, anything. Than you call the god, meditate before to get in a peaceful state and than call them, like a prayer, “come to me (name of the god)” than state your offering, something like “is humble but from my heart” and finally make you request “make him lose his job” or “got him sick” or “destroy his life completely” this will depend on what you want that happen to him. After that, say thank you. Wait a few hours or a whole day, go with your intuition and eat the food if was a food you gave as offering, or let the flowers wither if that was the offering.
During this ritual it helps if you draw a rune for your intention(change, destruction, justice, revenge, etc), Google it to find them. Don’t forget in create a protective circle around you before you begin, to do that all you have to do is imagine and believe that there’s a circle around you that will protect you against anything with ill intentions, say those words while doing the circle in you mind. You can light a candle too if you want to.
After that, forget about, there was one thing I asked and it took 1 month and only after I had forgot about it. They’ll find a way to show you the results, so no need of keep thinking about it or stalking his life.
In the meantime focus on yourself, the biggest revenge in the end of the day will be make him see what he lost. Don’t let him be in the way of your happines, after perfom the ritual you can’t have any doubt about if it will work or not, so just be sure that he will pay, that you did it, you revenged him and go take care of yourself. Focus on your work or study, in your dreams. It’s time for you fall in love with yourself, to heal. Find a new hobbie, change your routine, cut or dye your hair if you want to, just change things around you, listen to some power up musics to inspire. Buy yourself things. And cry, it’s okay to cry if you’re hurt, just be sure to rise up again smiling.
See you happy, smiling, beautiful working in turn your dream true will definitely be a plus revenge.
If you regret in make him pay through magic, which is okay, do the ritual again and when saying your requeste say to the god you called before that you’re thankful and sorry but you changed you mind, if you did the rune and still have the pape torn it apart, only after say the thank you and sorry to the god, undoing the spell. I think some gods wouldn’t stop if you regret, so be honest with yourself, if you think you could regret, be careful in choose a god that won’t mind and undo it. To find out this, just search about them, use the searchglass here in the forum to search about the god, google it, watch yt videos about, ask here. Make a wise decision. 
Hope this help. 