Don't ever regret THIS
Whether it's your boyfriend of three years with whom you didn't see a future or an old friend who stopped putting effort into seeing you, they made you feel happy along the way, so you shouldn't lament having them in your life.
What's more, you likely learned a thing or two from that individual. Maybe it was how to swim, how to cook, or the best way to approach your boss about asking for a raise.
Relationships sometimes end miserably, and there's nothing wrong with not wanting to see or hear from the person again. Still, you shouldn't regret the existence of that relationship, for it helped mold you into who you are today.
Perhaps it made you realize the kinds of friends or partner you really yearn for in your life. Sometimes we go through a bad experience with one person, learn from our mistakes, and have a much better experience the next time around.
That's precisely what happened with a girl I dated in my late teens. Though very attractive, she was very aloof and immature, and it drove me bonkers. Once it all ended, I vowed never again to get involved with an emotionally distant woman.
I felt like I wasted precious time with the girl, but I don't regret having met her. The experience taught me what I truly valued in a woman and, lucky for me, I have found those qualities in my dear wife.
Regrets should be reserved for things not done, steps not taken. At one point, you thought that relationship really had potential. No matter whose fault it is, take what you learned, which will stand you in good stead down the road.
As much as you may claim to hate this friend or ex, you may never forget them for the rest of your life. Instead of disparaging them, wish them well and move on with your own life. The future looks more than bright.