This happened a couple days ago and we are fighting about it and I just want to know if i'm being unreasonable.
So i've been dating Cora (my girlfriend, 25) for a couple years now and she just had her birthday. A week out, I asked her not to make any plans for her birthday obviously stating that I had made evening plans for us (dinner at this restaurant she's been talking about for ages, dessert and then a drive to go stargazing). I had been hinting around it all week to Cora. I also asked if her friends wanted to celebrate with her. They told me at the time they had "not figured anything out yet" so I assumed they weren't doing anything and then made my plans.
The day of Cora's birthday comes and she leaves in the afternoon. I thought no big deal, she was probably having some birthday time to herself. She hadn't posted on her story or anything so I didn't think anything of it. 6pm rolls around, I'd messaged and called her and still nothing so I checked her location because she normally replies very quick (we have each others for safety reasons) and she was at one of her friends houses. So I asked her friend if she'd seen my girlfriend because I had a birthday surprise set up for her.
Turns out that her friends did make plans for her birthday and didn’t tell me because they thought I would "ruin the surprise" and "wanted it to be a complete secret" They had lunch and then made more plans to go out to some bars and celebrate. They then invited me but I declined out of politeness and not wanting to crash their plans since she sees her friends rarely outside of work. I messaged Cora to have a good night with her friends and I'll see her when I get home (I had a cake waiting for her and thought nothing of it and hung with a couple of my friends).
Cora came home and was angry I turned down her friends invitation and she wanted to see me with all of her friends on her birthday too. I said it wasn't a big deal and that I saw her in the morning and when she got home anyway. I also said that the invite felt like an afterthought when she had all the time during the day to invite me and she didn't. Am I being an asshole here?