A person with whom your relationship is primarily sexual and romantic.
Lover is a title given to someone you are dating with whom you are infatuated and addicted to sex, before you are sure where your friendship is going.
If you add good friendship to lover-dom, you will probably end up with a Relationship or a partnership.
If are missing good friendship, the relationship will dissolve into fuck-buddydom or a complete break up.
Linda: What is going on with Mel?
Jane: I am not sure, but the sex is mindblowing and the world melts away when we are together.
Linda: Oh! The essence of lover-dom!