I had this happen IRL when I was at uni. Both myself and my best friend really liked one dude, who we hung out with as friends. She had originally intended to let me pursue him, since I seemed more passionate about it, but over the semester break they spent more time together (they both lived on campus) and fell for each other.
Having her tell me that when I returned for semester 2 was so hard for her, and horrible for me, but you know what? We dealt with it like adults should deal with it. She pulled me aside, told me, and apologised. I told her there was nothing to apologise for, wished them well, gave her a hug, and went off to the library to have a cry for a bit. Came back an hour later, and we remained best friends all through the remaining years of uni.
Had we been in a TV show, it would have been BETRAYAL, MORTAL ENEMIES NOW. Like, no. I couldn't control how he felt towards her, and why should she turn him down? Because I liked him? No. He didn't feel the same way about me. Not his fault. Not hers. Not mine.
Feelings happen. You need to learn how to deal with them maturely, and I think having more maturely-dealt-with situations like this in media, particularly YA media, is super important. (I'm definitely using it in my more YA-focused series.)