You have to tell me more so that I can give you good advice. How old are you both? Briefly, what is your sexual history, and his?
It’s definitely not normal for two adults to have no sex for 18 months in a three year relationship, so something is wrong. Sex is a normal drive for adults, and if you don’t have that drive there may be a biological problem, so getting a full physical and telling your physician everything is crucial to your situation.
In addition if you don’t talk honestly to your boyfriend this problem will get worse. You have to stop protecting him and yourself, and tell the truth if you want a healthy and happy relationship with him.
I look forward to hearing more from you so I can help you better. 🙂