Breaking up with a live-in boyfriend or girlfriend is much more difficult than ending a standard dating relationship--as well it should be. To do it, you must always remember to think of the other person's feelings first.
Act courageously. The first step in ending a relationship is having the courage to follow your heart. For those who have lived with someone and ended a relationship, perhaps the toughest part was just making the decision to end it. Following your heart means spending time alone and weighing the positives versus the negatives. Most people don't really want to be alone, and the comfort of a relationship--especially one in which you're sharing everything from dim sum to weekends on the Cape--can be especially alluring.
If you don't make a list of what you--not the other person--need in a relationship and analyze whether this person is giving those things to you, you're not helping anyone or going anywhere. When was the last time the two of you really laughed together? Are you arguing more than you are laughing?
Tell your significant other you two need to talk. This will immediately be a red flag for the person, and most women (at least) will be so suspicious they may automatically start grilling you about what the problem is. Sometimes men keep their feelings so tightly wound that they hardly want you to know they're hurting. A man may feign ignorance, but he, too, will sense this is serious.
Pick a time and spot for the talk you are about to have. Don't go to a restaurant because there will be people close to you and you want some privacy out of respect for the other person. Pick a park or the beach where you can be out in nature, where the mood is otherwise relaxing and there are people but they're not close enough to you to hear every shout or accusation. If you think you'll get out of this unmarred or that your partner won't yell at you, you're kidding yourself.
Set the tone. "I think you know why I wanted to talk," you might say. He might say no. He is probably hoping his gut isn't telling him the truth and that you aren't ending it. The important thing is to be as truthful as you can be while also being as kind as possible. There is no need to divulge every, "oh, I thought your best friend was so much hotter" or "I can no longer stand your mother interfering in our business" and so on. Tell the person how much she has meant to you, but don't tell her that someone now means more to you. However, if asked if there is someone else--and if there is--admit that. Don't go overboard, whatever you do.
Stay strong. Don't take anything back no matter how much your partner is screaming, yelling or crying. If he is verbally abusive toward you, tell him the conversation is over. Do not take abuse under any circumstances. If he is crying and truly upset, spend time comforting him. Do not take this moment to tell him when he must be out of the house or when you are leaving. That comes a little later.
Set a deadline. Finally, maybe three days later, tell her that you are leaving a week from today and you've made arrangements for the dog or the mail or whatever else you have to address. It is trickier when you have to ask the other party to leave. That said, give her a deadline and hold her to it. She may hate you for it, but eventually she will realize it's the best course. Most people will want to leave quickly anyway. For financial reasons, sometimes people have to stay longer. In that case, give her up to a month to get completely out, but during that time, do not give in to pleas, puppy-dog eyes or tantrums. Those last few weeks will be tricky, so don't be vulnerable. You've made your decision so stick to it.