Non_Passerine wrote:
I say "my parents were lovers for 15 years," meaning they were married 15 years before they divorced. Is that grammatically correct?
Grammatically it is correct but it isn't correct if you consider the meaning.
It would only be correct if they were strangers before getting married, they fell in love around the marriage time and they loved each other till the divorce or if they fell in love for example 3 years before the marriage but the love expired 3 years before they divorced.
If they were dating/loving each other for some time before the marriage and they loved each other till the divorce you add the time they were this way to the time they were married. So if they started a romantic relationship 3 years before marriage and they loved each other for the whole time they were lovers for 18 years.
Lover doesn't mean spouse. It means someone you are in romantic relationship with, someone you love and who loves you. It might be a spouse, a partner, a boyfriend, a girlfriend etc. but also someone you secretly cheat on your spouse with.