Kinda petty but I would appreciate advice.

So my workout friend who I’ve known for a while now got a boyfriend. We are only 15 so I’m just trying to figure myself out before getting into anything. I go to the gym on Sundays bc that’s when I get the best energy. My friend recently started going with me. Saturday’s I’m usually doing something with family or doing homework. I always go on Sunday’s but keep in mind I a) pick her up and drop her off, my mom doesn’t mind and thinks it’s good bonding time lol, and b) my mom is available to take me and sometimes her Sunday’s. So my problem, She texted me 10 minutes ago saying she forgot that she made plans with her boyfriend for Sunday and asks if I can do Saturday instead. I don’t know what’s going through my head or if it’s my period but I just get upset because she rather sacrifice my time for her new man. I just need someone to tell me if they have had similar situations. Pls no hate I am kind of jealous but it’s whatever. I’m not trying to be an obsessive crazy friend. She says they are seeing a movie Sunday. Keep in mind, SHE texted me asking to hangout Sunday/go to the gym and then forgot that she made plans with her boyfriend, but I’m thinking they probably reserved seats already. I feel mentally exhausted from having to work around her time because she forgot she already make plans with her bf. So what would you do, should I say no I’m going Sunday. I kinda just wanna teach her that it’s okay to forget but I’m not working around ur schedule, like people find other people but don’t expect me to be there when ur available...