I despise people like this... I understand liking someone, especially your friend, hiding it from them, and being a tad bit hurt when they love someone else. But I never tried to ruin their relationship, I was happy for them, and sad I let myself love (romantically) somebody I once saw as a friend. I got very tired of seeing my friends that way, I wanted a platonic friendship. I liked them but didn't desire to date them, because I knew my feelings if anything where temporary, and that I committed to a friendship not a relationship. I was never really jealous, and never bothered by their partners, I was happy they introduced them to me, because that ment they trusted me. But I NEVER tried to frame them into thinking that their lovers where bad for them or used them when it wasn't my business. I have fallen for many of my friends, at least it's like falling for them, but I don't think I loved them, I got over them too quickly because all those friendships ended. Whether I loved my friends in a romantic way, or if I just cherished them wayyy too much. It doesn't matter. Don't ever try to sabotage a dear friend's relationship. It hurts, but I never intended on confessing nor dating, because it was a fantasy that wouldn't ever happen. I knew they weren't for me, people come to pass in life, so you must let them go. "If you love someone, let them go" sh** I let go of all the friends I've loved. Sorry for the rant....
The point is don't do what Subaru did here, I know many lovers started as friends, but if you are in a situation where it's one sided, focus on you, understand that the relationship you desire with them won't happen, and if it does it won't turn out well. Let go of your feelings and cherish them for what they are. Your friend. :)
Peace.