Masturbation usually has nothing to do with how much love there is in a relationship. Of course, there might be a correlation with a lack of affection if one partner is denying the other sexual access, or if the two partners are emotionally estranged. But most of the time masturbation is just another way of solving old-fashioned, physiological horniness. Look at it this way: The better sex is, the more someone wants. In other words, the better your sex life, the more sexually turned-on you and your partner are likely to be. What this means is that when you have an orgasm, it builds the need for more (after a suitable pause, of course). The less sex a person has, the less urgent the desire for more sex. I know this is counterintuitive, but it’s true. So, actually, masturbation is often likely to occur in a relationship that is not only sexually adequate—but sexually superlative.  The additional sexual need has nothing to do with love, but rather with increased appetite.

Masturbating really has nothing to do with how much attachment there is in most relationships.

from Everything You Know About Love and Sex Is Wrong: 25 Relationship Myths Redefined to Achieve Happiness and Fulfillment in Your Intimate Life