AITA for hanging up after i was uninvited from a birthday dinner?

for context this is a dispute between me and my bf, we’re both 22 and have been together for nearly 3 years. his parents are divorced, mine are together. we’ve gone to see my parents loads and loads of times and they love him like family. i’ve only met his dad one time two years ago for half an hour and i’ve never been allowed back since. additional context his dad is terminally ill and was given 12 months when first diagnosed but again this was 3 years ago and he’s doing very well.

so the thing that’s properly set me off is that it’s my boyfriend’s brother’s birthday in a few days, and a week or so ago my boyfriend (call him Sam) invited me to go out with his brother (call him Max) and his brother’s girlfriend (call her Rose) for Max’s birthday. i said that sounded fun because i get on really well with Max and Rose. we’ve not spoken about it since then so i assumed all was fine. then i got a call from Sam telling me he was going Max and Rose’s city tomorrow and staying there until friday to celebrate Max’s birthday. he told me that he’ll be back on friday morning. no mention of me going with him, to which i asked him what their plans were for the actual birthday. Sam said him, Max, Rose and their dad are going out for a meal.

i think i must have sounded a bit upset because Sam asked me what was wrong, i told him that it hurt my feelings a bit that he jus sprung it on me that he was leaving and didn’t acknowledge the fact that he invited me just last week, to which he said that invitation was only if they were going out drinking on Max’s birthday, but since the plans are now going for food with their dad, i am no longer invited.

without sounding like a terrible person, i’m quite pissed off. my boyfriend goes to visit his dad quite frequently (around once a month) and i was allowed into the house once to use the bathroom. i’ve never really spoken to him, i was inside their house while waiting for Sam to be ready to leave but i was mainly speaking to Rose (because i tried to make convo with their dad to absolutely no avail, he just gave either one word answers or totally ignored me). i understand that he doesn’t feel well a lot of the time and he doesn’t want to speak to a new person, but we’ve been together nearly three years and Rose literally lives in their house with Max and their dad.

i make a big effort to always include Sam in my family activities, he comes to most family parties and he even went on holiday with my family last year. literally if i give Sam a lift to his dad’s house i have to drop him off on the road and find something else to do until the visit is over.

am i being insane for being a bit upset about this? i feel like i’m being petty because his dad is ill but i’m not asking for a flipping sleepover i just wanted to meet them at the restaurant, eat and go back to my city because i was invited to do so! anyway please give me opinions because i am so torn

EDITED FOR CLARITY