Ok, endless sex scenes are a sure way to turn me away from a story, too. As for reading endless stories to the finish - I just don't do it. I love long stories, actually prefer them, but it should be one long story imho, not an endless number of stories of an endless number of characters. I also really dislike soap operas, so I guess I mostly agree with you. I didn't finish the Lightning Arc because it went from pleasure to pain, which I sadly have to say about the second part of "Cambiare Podentes", about "A Year Like None Other" and some other pretty well liked stories; but also about some fantasy books like RRMartins whatsitsname, or sadly, Robin Hobbs Liveship trilogy (though I still want to finish that one, some day).

I feel that a story is still ok as long as you can look at any part you've already read and figure out pretty quickly what it was about. If you really can't remember, or feel you don't care, it might (personal quirks set aside) be an indication that the scene was mostly meaningless, or useless.