Red yarn (about a yard will work)
For this kind of work (getting rid of an unwanted lover) I prefer to use a spicy incense like cinnamon or ginger. I also like to use the candles in the shape of people, but if they are unavailable to you or you have a preferance for using regular taper candles, that's fine too. The color selection of taper candles should be made inaccordance with who the two people are, both gender-wise and sexual preferance. For two gay men, I would use two brown or bronze candles, for two lesbians, pink ones.
I don't use a circle or "sacred space" when working with spells for purely mundane reasons, so I'm not going to include directions on how to set it up. If you prefer to use one, go right ahead.
Light the incense, relax, and let your mind think casually about the topic and work at hand. Pay attention to how you feel about the people involved and why this needs to be done. When you're relaxed and confident that you've got your goal firmly in mind, bring out your two candles used to symbolize the couple.
Wind the yarn around each candle (one end of the yarn for each candle) until they are about 6 inches apart. I like to wind it from top to bottom and then back to the middle, mummy-style. Set the candles (in holders, please!) on a table to other such fire-proof stable flat surface.
Focus in on what your goal is again. Sit and think about how you want it to happen, and the reasons it needs to happen. Place your hand on the bit of yarn between the two candles (it should be held tightly between them with no drooping) and focus in on your intent and say something along the lines of "When this yarn burns through, the love between these people will be done." Obviously, you can change the words to suit your intent more perfectly. If you have a liking for poetry (which I do NOT) you can even work up a line or two.
Light the candles, and let them burn down until they burn through the yarn. This will be very messy since there is yarn wrapped around them, so PLEASE do NOT walk away... It wouldn't be a bad idea to keep a bucket of water or fire extinguisher handy. It's always better to have a failed spell than a burned down home.
When the candles have burned off all the yarn, put them out and take each one seperately and either throw them in running water (like a river) or bury them. Do not throw them in at the same place, and do not bury them at the same place.
Go home, clean up, take a hot soapy shower, and go about your usual routines. Don't spend a lot of time focussing on this, just accept that it is done and will happen.