Sex is not and never has been a necessity, it is a basic human desire and nothing more. Though it is a desire that is natural and should be present. If it isn't then more often then not a medical condition is present or another problem.
Stress is often the most common cause of non desire for sexual relationships. Though hormonal imbalances and other medical conditions can cause this as well so it is always recommended that you first speak with your doctor to ensure there is no underlying medical condition causing the problem.
The next question is how do you feel about your boyfriend? The reality is if you are not in love with him, or feel no attraction toward him then the desire to have sex with him will not be there regardless of how much you want it to be.
The fact that you were in a loveless marriage for so long has set you to over sensitive when it comes to seeing a problem in current relationships. If there is something that is missing with your boyfriend then this will effect your sexual desires.