ugh please help

so back in september this kid took me to homecoming. (let's call him Chris) i was pretty into him and we started dating after. we dated until about january, and then over our winter break i didn't get to talk to him at all (i was in the middle of mexico doing humanitarian work, so i didn't really have wifi 😂), and when i came back he was different. we never went on another date and in our classes we had together he never really talked to me. it really sucked to see us drift apart, but that's not even the worst part. in april we had prom and my best friend didn't have a date, so a friend of mine suggested chris take her. i was a little upset that he took her, but they just went as friends so it didn't super bug me. a couple weeks later i wanted to take this kid on a date and my best friend suggested we make it a double. i agreed and asked her who she was bringing. guess who? yeah... chris. i asked if she could bring anyone else and she tells me that she really likes him and wants to start dating. she's gone a quite a few more dates with this kid and she keeps gushing to me about how great he is. is it wrong for me to be upset? she knew how much i liked him and she knew that we kinda had a falling out. i feel like here's a girl code rule that she's breaking but i don't know if i should tell her that it makes me uncomfortable that they're together now.