break up

Have any of you guys lost a friend before because they were in a relationship? It sucks. My best friend (if she even ever was) got a boyfriend and firstly he's way older than her, shes 14 and hes 17, and secondly they hang out all the time. Like I was meant to hang out with her at the park and then she asked if her boyfriend could come and I was like yeah sure but I didn't want him to. And then the whole thing was ruined beacuse I was in such a shitty mood and even though he was nice it was still awful. I just feel like I always come second in people lives, like they always have a best friend, or someone closer to them. And then I was this girls best friend but now I come second again. I don't know how to make this feeling go away. Has anyone else felt like this?