Well, right off the top, of course, is the series of novels by James Galloway, more commonly known as Fel, if you haven't read them. https://forums.sennadar.com/index.php The sex does distract from the story line, in my opinion, in the later volumes, but arguable based upon the society he's designed for that series. He does attempt to keep it from becoming too formulaic. In that series, the first volume is definitely the best. Too many rabbits get pulled out of hats as the series progresses for my happiness. But if you haven't read Subjugation, do give it a try; the interaction between the male MC and the female alien marine is quite fun, as she pursues and he evades; true love does win out in the end, but only after some fairly amazing things occur; he's an engineering student learning the alien technology in school, and comes up with some sweet applications of it that they hadn't thought of, very embarassing to some of the occupation's troops; well, if they had body modesty, which they don't. His science wouldn't work in the real world, but he makes it self-consistent, which is all I ask of in non-hard SF.