The 1981 version did seem to have a happier ending in comparison to the book. At the end of the 1981 version, Jade confesses to her mother that no one will ever love her like David, and, the last scene shows her walking towards David while he's in confinement. I, at least, find that to be a happy ending. Perhaps Jade never lost David and David never lost Jade. I got the vibe that they ended up together once he got out -- however long that may have been. Hence, the title of "Endless Love"
Off topic, but, "The Notebook" is one of my favorite movies, and, I didn't like it at first, either. When I saw it the first time, I was all "Meh" about it. Second time around, it grew on me. Third time around, it touched me in a very deep way. Now, every time I see it, I just fall in love with it all over again. Oddly enough, when I first saw the 1981 version of "Endless Love", I didn't like it much at all. Then, I saw it again, and fell in love with it. For some reason, I learn to appreciate movies way more on my second or third time watching them. So, if you didn't like "The Notebook", I'd honestly give it another chance.
But, then again, I am very partial and biased to these sorts of movies. Right now, I'm currently in a four year relationship that burns with a lot of passion. So much so that it truly is an endless type of love. Having experienced that gut wrenching, obsessive, passionate, consuming type of love has truly made me a sucker for movies full of intense and "crazy" loves. Has love driven me crazy? Absolutely. In both good ways and bad. I have been on both ends of the spectrum. This is another reason why I much prefer movies with "crazy" types of love. The original "Endless Love" and "The Notebook" both have scenes where people literally go mad from love. They love someone so much that it just tears them down, strips them away, and leaves them feeling hopeless, desperate, and full of tremendous longing and desire... I've been there, done that.
Hence, my issue with this movie is the same as yours. On top of it not resembling the original "Endless Love" in any form or fashion, the two main leads do look like they could be part of a toothpaste commercial. The whole movie looked like one giant toothpaste commercial, come to think of it, hahaha! It's hilarious how you pointed that out.