My friends are constantly telling me that they have multiple orgasms. Masters and Johnson demonstrated that women are capable of multiple orgasms, but most women are happy with one. So you are normal and healthy and just enjoy what you have. There are approximately 5,000 different things that can bring on a lack of desire including problems in the relationship, problems in the perception of oneself, problems in daily living, yada yada yada. The important thing is that the two of you schedule time to be close and intimate, and if that does not work, then you might want to see a therapist.
Sex is definitely a skill, and like any skill, it is refined with education and practice.
Humans have a natural sexual desire, but unlike bugs and rodents, there isn't a prescribed way to do it. There is a high educational curve. The more you read and the more you experience it, the more you will know. That is a wonderful question for which there is no concrete answer. Therapists are divided on what constitutes cheating.