my best friends took a different friend on holiday

for some context I have a trio and the other 2 members of my trio are twins. We have been a trio since 2021 and we get along rlly well. Last year this girl they were friends with in primary showed up bc i guess she had a falling out with her friends and at the time me and the twins were in a group of i think 6. For the sake of anonymity i’m js gonna call her new girl so new girl shows up and my dad had just died like 3 or so weeks ago (important for later) but i don’t think anything abt her joining. however she then starts acting like super close w one twin like kinda walking slightly separated from the group and constantly link in arms and i think it’s a bit odd but again not that much until this twin starts an argument w me over smth very small. Obviously due to my dad dying very recently it’s not a good time whatsoever and bc the argument was so petty and at probably the worst time everyone who knew abt it was telling her this is wrong and the only person siding with her was new girl but she was rlly set on being right and that I had to apologise but I wasn’t gonna do that due to everyone agreeing i’m not in the wrong here and so it lasts a few days and eventually she apologises and i forgive her but it does definitely put a bit of a dent in our relationship for a few months. in the days after she apologises I notice new girl will just randomly be like omg are you ok do you wanna go walk even when said twin is js like listening to conversation or smth and not showing any signs of being sad and ofc i find this weird and her being the only person to side with said twin kinda made me not like her but she’s in the group so I js try to ignore her. As time progresses with her in the group I kinda find that the majority of the conversations she starts is about primary school or the years of middle school before i joined (i joined that school 2 years after most other people) and there was another girl in the group who was at that middle school for the 2 years before me but left the year I joined. I find this really odd bc it’s not just a few conversations it feels like 75 percent or more of the conversations involving her are abt those years when i wasn’t there and again this pisses me off more but i js tolerate it. She kinda does this until this year she left school and by this point all but me and the twins and one guy was still in the group and i’m a lil relieved yk and life is good up until now. Js before i tell the part abt why i’m angry I think it’s worth mentioning that I often try do fun things w the twins and bc we r all kinda poor but them a bit more than me there’s times when I decide to pay for them for smth fun like we went to see coldplay tg and I ended up letting them go w me for free js bc I thought it would be fun and for my birthday we went to a 5 star hotel for the night. I don’t mind doing these things bc I enjoy them and ik they do too but it does take a long time to save up bc I am so poor. Now the part that happened this week. Every year the twins go away in summer for abt a week and usually it’s with family friends. This year however I get a text a few days ago saying they are taking new girl on this holiday with them and they didn’t think I wanted to go so they didn’t invite me and I was like why did u think i didn’t want to go not mad i’m js wondering and they were like well you usually struggle on sleepovers and you just don’t seem like you’d like it much. For that day i’m kinda rlly upset then the next day I kinda think ok i’m gonna tell them that this upset me a little bc they didn’t ask and everyone always says sayinf we didn’t think you’d want to go often means they js didn’t want you there and this convo was kinda between js one twin bc the other seems to have a closer relationship with new girl and I just said i was hurt bc this year they just assumed but also bc we had been friends since 2021 and I had never been asked and she did kinda give some reasons as to why they thought i didn’t want to go but also I still had that inkling that I wasn’t the first choice so I confessed that ever since new girl joined I had been feeling like she was trying to replace me and I confided in another friend and she agreed that new girls behaviour was definitely rlly weird towards me and I js feel like sometimes they prefer new girl over me (more so the other twin) and I felt better abt it for a few days but now I js keep thinking abt how they didn’t even ask and how it felt like I wasn’t the first choice and also I didn’t tell them this but especially this year I had done so many things for them that meant I had to be poor for weeks to save up for it and I’m not saying they owe me anything but idk it just hurts a little that I sacrificed sm and now there’s an opportunity where they could kinda do something of the same nature yet they chose her instead of me. So am i the asshole for being upset about this (if i am pls be nice abt it i’m kinda upset rn )