Breaking up is hard to do--especially when you've been in love with someone, or at least told someone you loved him. Men and women may lash out in anger, cry or engage in other shows of emotion. Even though dealing with such animosity is difficult, you need to face the situation head-on. Telling someone you don't love her anymore is something you do in person, not via voice mail or text.
Tell your significant other that you have to talk. He will immediately sense what you are driving at, whether or not he wants to admit it to himself. The longer you wait to do this, the harder it will be.
Make the environment as comfortable as possible without adding romance to the equation. Don't opt for a candlelit dinner or a drive down the Pacific Coast Highway, past that stretch of Santa Monica where you rekindled your love one warm September night. Instead, tell your partner you want to spend the day outdoors or having a casual lunch--perhaps at the mall. Food courts are anything but romantic. Just make sure you have an area more or less to yourselves, in case she starts to throw French fries at you.
Grab his hand. This may seem to run counter to what many relationship therapists would advise, but guess what? Touch soothes us. Holding someone's hand is non-committal, and it's an homage to the love you once shared. Don't worry: He will be yanking that hand away soon enough.
Spit it out. Say, "I am not in love with you anymore." Don't insult her by saying, "It's not you, it's me," because it's not. It's her--and if she were the new woman you met on MySpace or at work or wherever it is you think your soul mate resides, you wouldn't be having this conversation.
Maturity will tell you that real love is very rare, while infatuation is an everyday phenomenon. Chances are, you'll never have one meaningful date with the new gal; but years from now, you might rue the way you ended this one. So think it over carefully.
If you don't love her anymore, though, say it now. Spit it out. This is a bandage-off approach and must be taken.
Allow his emotions to pour out. Some men can't stand to show vulnerability, and may get angry, storm off and/or accuse you of being a philanderer. Women may weep and punch you in the arm. Anything can happen. But let's assume you aren't dating a psycho. It's most likely, then, that your significant other will show a reasonable amount of emotion, storm off and ask that you leave him alone.
Let her go. Don't call. If she calls you, you should naturally talk to her--especially the first one or two times. If you have stuff at her apartment, you'll have to arrange to pick it up. (You get extra points if you remembered to retrieve some of that stuff before making this admission.)
Don't drag it out. "I no longer love you" means you are no longer invested in the relationship.
If you feel you are simply in a mood, or you are dealing with some kind of crisis, that is a different matter entirely. In such a case, you both should try couples' therapy.
If your significant other is unstable, make sure you have a friend nearby when you break up.