Are there any legitimate romance series that follows one couple (or at least the same protagonist) over multiple books? And can that work well without losing the audience's attention? I'm not referring to series with heavy romance elements or romantic subplots, but actual romance as the primary genre. I've seen things labeled as romance series that usually just focus on the romance of a different protagonist in each book. Usually, a group of siblings or friends, because you know romance is contagious. This is probably true to life since both of my husband's best friends got married and started having babies soon after we did XD.

I guess the problem that would arise is romance usually is required to have a HEA or HFN. If that doesn't happen until the end of the series, would that mean all the other books in the series aren't romances?