Unrequited Love Switcheroo/Playing With

Basic Trope: Someone loves someone else, but their love isn't returned - until they enter into another relationship.
 * Straight: Bob is in love with Alice, but she doesn't return his feelings. When he gets into a relationship with Carol, she falls for him.
 * Exaggerated: Every part of the Love Dodecahedron flips when someone enters a relationship.
 * Downplayed: Alice wasn't entirely oblivious before, but once Bob and Carol become official she realises she's jealous.
 * Justified: Alice didn't realize she loved Bob until he wasn't on the table anymore.
 * Inverted: It's not until Bob's in a relationship with Carol that he realises he loves Alice.
 * Subverted: Bob gets into a relationship with Carol. Alice is glad because that means he'll stop trying to pursue her.
 * Double Subverted: But after a while, she realizes she secretly enjoyed being pursued...
 * Parodied: Alice openly and repeatedly mentions her vitriolic hatred for Bob - until he gets into a relationship, when those feelings are replaced with slavish devotion.
 * Zig Zagged: Will They or Won't They?.
 * Averted: Alice just plain isn't interested in Bob, before or after his new relationship.
 * Enforced: "OK, we've dragged out the Unresolved Sexual Tension between these two enough, but how can...wait, I've got it! Let's have him get into a relationship with someone else!"
 * Lampshaded: ???
 * Invoked: Bob starts hanging around with Carol in the hopes of getting Alice's jealousy working.
 * Exploited: ???
 * Defied: ???
 * Discussed: ???
 * Conversed: ???

Back to Unrequited Love Switcheroo. Funny, you didn't seem very interested in it until it started dating someone else...