I know what you mean! Summer's Desire was epic! :) I'll reccomend you some dramas with very persisting 2nd lead ;)
My Love Eun Dong - modern k-drama - both leads are crazy in love with female lead. The second lead use very selfish way to get the girl and manipulate her and lie to her. It's a true war between main leads but with a very touchy story :)
Delightful Girl, Choon Hyang - modern k-drama - the 2nd lead is older and richer than they younger main lead, so he uses it to get the girl, tries to manipulate and force her to be with him. I foundit in some way similar to Summer's Desire.
My Sunshine - modern c-drama - the 2nd lead comes later, but he's very persisting and use dirty tricks to get the girl that once was her for a short time. It's a complicated story, but the jealousy scenes are very satisfying ;)
Sound of the Dessert - at first it's not obvious who is the main lead here. Both guys are crazy in love with the girl until the end. It has a great romance and chemistry between main leads :)