Omg some of these replies are ridiculous. Of course it's unreasonable! If this was a man posting on here saying that the mum had gone out for 3.5 hours on their daughter's first birthday, everyone would be up in arms!
It just shows that some people have really low standards from men / their partners / father of their children.
OP - of course you're not being unreasonable. It doesn't matter if you had absolutely nothing planned - it's your child's first birthday. They don't get another one. It's not about whether they remember it either, YOU will. And for one of their parents to disappear for 3.5 hours to do something that is absolutely unnecessary that could be done on any other day of the year, is out of order. It shows you where his priorities are!
I bet you wouldn't dream of doing that, so why is it okay that her dad did? I'd be upset if it was my partner too!