Most human beings seem innately averse to change. Once we've established some measure of comfort or stability, we want to nail it in place so that there's no possibility of loss. It's understandable, then, that the promise "My love for you will never change" is a hot seller. Unfortunately, this is another promise that is more likely to scuttle a relationship than shore it up.
The reason is that everything—and everyone—is constantly changing. We age, grow, learn, get sick, get well, gain weight, lose weight, find new interests, and drop old ones. And when two individuals are constantly in flux, their relationship must be fluid to survive. Many people fear that if their love is free to change, it will vanish. The opposite is true. A love that is allowed to adapt to new circumstances is virtually indestructible. Infatuation relaxes into calm companionship, then flares again as we see new things to love about each other. In times of trouble and illness, obligation may feel stronger than attraction—until one day we realize that hanging in there through troubled times has bonded us more deeply than ever before. Like running water, changing love finds its way past obstacles. Freezing it in place makes it fragile, rigid, and all too likely to shatter.
3. You're not everything I need.
I'm a big fan of sexual monogamy, but I'm puzzled by lovers who claim that their romantic partner is the only person they need in their lives or that time together is the only activity necessary for emotional fulfillment. Humans are designed to live in groups, explore ideas, and constantly learn new skills. Trying to get all this input from one person is like trying to get a full range of vitamins by eating only ice cream. When a couple believes "We must fulfill all of each other's needs," each becomes exhausted by the effort to be all things to the other and neither can develop fully as an individual.
It amazes me how often my clients' significant others feel threatened when the clients revive childhood passions or take up new hobbies. I encourage people to bring their spooked spouses to a session so we can discuss their fears. The hurt partners usually come in sounding something like this: "How come you have to spend three hours a week playing tennis (or gardening or painting)? Are you saying I'm not enough to keep you happy?" The healthiest response to such questions is "That's right, our relationship isn't enough to make me completely happy—and if I pretended it were, I'd stunt my soul and poison my love for you. Ever thought about what you'd like to do on your own?" Sacrificing all our individual needs doesn't strengthen a relationship. Mutually supporting each other's personal growth does.