my personal favorites aren't love triangles, but love stars, where multiple people fall for one individual, who may or may not be interested in any of them but still doesn't pursue a relationship. (Person B likes person A. So do persons C, D, and E. Person A likes person C). B, C, D, and E unite in their mutual infatuation w person A and become best friends. As they scheme to win over person A, a mysterious, powerful individual, their bond becomes stronger. They realize they are in love with each other. Person A is revealed to be a real asshole, but the others don't care anymore. They are happy together -- as friends, or as something more? (cue dramatic music)
Make something new of it! Like, a writer I heard about recently released a YA novel about a teenage boy who falls in love with his bigger sisters boyfriend/date/flirt/whatever. It doesn't have to be cliché. That said, the scenario you presented doesn't sound very nice. Why would he be with someone he's not in love with and what's keeping him from being with the sister instead? That kind of scenario would make me lose interest in reading it, I think.
I think it's real life, actually. Many people (whom I've known) make a premature committment to somebody whom they think they love, but when they actually meet the person they DO love, they are reluctant to hurt the person they've committed to. In your example, both the guy and the big sister probably want to spare the young one any pain, so they will probably resist their own attraction at first, or decide to sacrifice it. As long as this doesn't get too soapy (will they, won't they, will they, won't they, tease tease tease ad infinitum) I think it's a topic that's well worth writing about. It's a decision many of us will face during our lifetimes. Do we put our own happiness first, even if it means hurting somebody else? And if the person we may hurt isn't with a person who actually loves them, aren't we actually doing them a favour taking the 'mistake' away and giving them a real chance at finding love? Good questions for a writer to ask.
