Question about my friend (who I kind of like)?

You should be more concerned with why an 18-y-o guy is dating a 15 year old. I think he probably just umed he had a better shot with the younger girl and didn't want to risk getting hurt. Make your intentions for him more obvious? Guys in high school are f*cking oblivious when it comes to this stuff. My real advice would be to just find another guy. Don't waste your mental energy dreaming up these scenarios when you can be out and enjoy being young and attractive.