Lovingkindness is a basic Buddhist concept, one I've found to be very important when one is doing the painful, scary and difficult work of becoming sexually whole and integrated. It works in all other areas of spiritual inquest of course, and in the context of Sex Positive living we’ll apply it to our sexual selves.
Lovingkindness is what we use when we find ourselves upset, angry, frightened, despairing, lonely, horny, judgmental and hurt, be it about sex or anything else. It’s a set of behaviors as well as a mindset.
I'm not religious but when I was ten my parents became dedicated students of Zen Buddhism. Their teacher, Shunru Suzuki, was the man who introduced Zen to the US in the mid-1960's. His most famous book, "Zen Mind, Beginner's Mind," was very influential in my life and I use these concepts when dealing with life's inevitable painful moments. Over time I’ve found them to be very effective. The concept is simple but not always easy to apply, since we’re fighting uphill against our conditioning. It’s only when we start to use lovingkindness that we see how far our daily lives have strayed from it.
The Dalai Lama has said, "There is no greater wisdom than compassion." I've found this to be true. As we gain awareness of our own emotional processes we learn to recognize when our feelings are rising to the point of us losing control over our behavior. Until we do so we’re often faced with having to apologize for doing or saying something horrible or mean, which we then have to take back. Often, the damage has been done and apologizing does little to address it. When faced with the choice to either lash out in anger or pain or remain silent, most of us choose lashing out. We do it out of habit and don’t realize that it’s really our hurting “inner child” crying out for our attention.
Until we can head off angry behavior at the pass, we’ll often be left to deal with the aftermath of a blowup. When this happens try to get a little distance from the incident with two or three breaths and then attend to that hurting inner child with the compassion that's been missing up to this point. When we do this insight is gained, pain is released and love gets a toehold. Since we're often in painful situations we have many opportunities during the day to extend to ourselves the compassion we need. Usually, all an intense emotion needs in order for it to calm down is simple acknowledgment of its existence and value. At that moment nothing needs to be done except understand what just happened, and why.
It’s helpful to keep in mind that all feelings want is to be acknowledged. If they can’t get your attention quietly they’ll act out until you do pay attention, even if it means embarrassing you in front of your lover(s). We can’t hide from our feelings no matter how we try so we might as well turn and look directly at them and how they influence us. Of course, this takes time and countless moments of embarrassment until we decide that the old way isn’t working any more (if it ever did). At least, it worked this way for me. I was incredibly stubborn and resisted this fundamental lesson for many years. In the end, I learned the lesson the hard way when I could have learned it the easier way.
How might you be embarrassed by hidden feelings? You may fall asleep in the middle of lovemaking. You may disassociate from your body and mentally and emotionally be far away until you’re called back abruptly. You may lose desire for sex with your partner, or even for masturbation. You may say something disparaging, snarky or snide before you can clap your hand over your mouth. You may be unable to get aroused or have an orgasm. You may call your lover by the wrong name. You get the idea.
No matter the source of our upset, fear, panic or anger, lovingkindness is the antidote for that difficult moment. In the moment of emotion, logic is useless and one must speak directly to the heart of the matter, feeling to feeling. Meeting any so-called "negative" emotions-anger, jealousy, fear, panic, grief and more, with another "negative" emotion serves only to make things worse. No, the feeling that will be most effective to change things in the moment is compassion, lovingkindness, acceptance and understanding. Once the "negative" emotion has been seen and recognized it can, and does, dissipate rapidly. To quote Cheri Huber, "What you resist, persists."
Our sexual lives often thrust us into the very heart of our deepest fears. If we use our sexual expression consciously we can scare ourselves juuuust enough to keep us on our toes but not so much that we skid out of control and hit the trees. Being compassionate to ourselves when we're scared like this reaps great benefits. Sex is good for this kind of inquiry since it's portable, universal, needs no batteries and can be turned on and off as need be. Plus, we can scare ourselves in exactly the right way, for exactly as long as needed, as strongly as we require, for the good to be done. Ah, the benefit of sex are neverending!
Lovingkindness starts with ourselves: we never put ourselves into situations where we may come to serious harm. We make sure we're safe and then give ourselves permission to dive in fully into the moment. We also don't use sex to harm another person's body, mind or spirit. We do our best and don't beat up on ourselves for being human but we don't indulge our weaknesses too much, either. As a wise person once said, “Forgive yourself everything, but not in advance.”
Most sexual pain is due to cultural conditioning, something over which we have no control, so we must be kind to ourselves as wake up to our lives as they are and not as we think they should be. In fits and starts, lovingkindness smoothes the way for growth and happiness, and sexual pleasure is the vehicle by which it can happen.
How do I exhibit lovingkindness during sex? Simply by welcoming my partner (and myself) in all of our naked glory. By being generous. By being patient. By being kind. By communicating clearly. By keeping my boundaries secure. 
It takes practice and it's worth every effort and it totally works over time.