Am I being childish?

My flatmate and I used to do quite a few things together. Now we have a new flatmate, they are both smokers and they spend a lot of time together. To be honest they are bonding over a really bad habit and I’ve noticed my flatmate smokes a lot more since our new flatmate has come. Hmm.
I just feel a little left out. I’ve noticed that my flatmate doesn’t stay in the room with me like before, nor does she initate much convo. I’ve always been nice to her but her behaviour had changed.