What different levels of desire means to me is that 2 people's sex drives differ. In other words, one wants to have sex more often than the other. To me sexual incompatibility means that two people differ in what turns them on; they differ in just what sexual activities they prefer and possibly how to do them. For example, one person may be turned on by sucking a partner's toes, but the other person doesn't want to be the toe suckee or sucker. Maybe one person really loves anal intercourse but the partner has no interest in that activity whatsoever. Or maybe one person is greatly turned on by BDSM, but the other person is strictly vanilla.

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Communication is the key.