If you say you have a lover, that means you are in a romantic relationship with someone, and you feel confident enough to say he is YOUR lover. Married people can be lovers to, and I hope they are.
If you call someone by a name like "hello, Sweetheart" "Hello, Honey", "Hello my Darling", "Hello, my Love"....you could be talking to your spouse, lover, child, very close friend, etc. Women often use these sweet "nick-names", and men will call their girl friend or wife sweet names like this also.