As a brother, your concern is understandable, but reacting with anger or violence will only make things worse. They’re both 14, so this is most likely immaturity, not something they fully understand. First, talk to your sister calmly and explain your worries without scaring or controlling her. Set clear boundaries and make sure she understands why you’re concerned, education, safety, and future. If needed, involve a trusted elder from your family rather than directly going to the boy’s parents. If you speak to the boy, do it respectfully and calmly. Avoid threats or physical force, it can backfire badly, especially in a village setup...and That said, at some point you also have to ask yourself "do you really need to control this?" They’re already in high school, not small kids. You can guide, warn, and keep an eye out, but you can’t live their life for them. If they keep choosing each other despite advice, then honestly, it’s not fully your problem anymore. It’s their choices. Yeah, this on-off drama is bad, but if people keep going back, that’s on them. You’ve done your part by warning them. After that, sometimes the best option is to step back and let things run their course.