Is this your first baby, OP? I think people forget that having a baby is a major trauma, both physically and mentally. A lot of women can barely stand or hold their babies straight after delivery. Giving birth is bloody exhausting too, and you would absolutely not be unreasonable to need lots of support in those first hours. It's at that time that you're most vulnerable too and I know I certainly wouldn't have wanted anyone around me but my DH at that time. I tore terribly, my stitches ripped, and I was in so much pain and bleeding everywhere. Baby was pretty much attached to me the whole time trying to breastfeed and I was having trouble getting her to latch so then I got upset, and the whole thing was incredibly emotional. You wouldn't have been unreasonable in the slightest expecting your oh to be with you for as long as needed to comfort you, watch baby to make sure you had some sleep to recover before visiting hours were over (for me those first days in hospital were hell. There's no chance of any sleep and you're already so exhausted from the birth and you're on your own and in pain and barely holding it together!!!) and he should have made sure you were fed, comfortable and ready, physically and mentally, for the following hours where you'd be on your own.
At 9 the child should be old enough to understand that his dad would have to be elsewhere but it didn't mean he didn't care. Hopefully, all things going well during the day there's no reason why the dad couldn't have then spent the evening with his son, possibly nipping back to the hospital before the end of visiting hours to check in and make sure new mum and baby were ok. If handled sensitively there's no reason why that couldn't have worked and lots of fuss being made of the soon then.
On saying that, if the birth was particularly difficult then you may even have been justified in wanting the father there with you the whole day. With my second the gas and air triggered horrific migraines and for the first week I could barely even see my baby, let alone hold or look after him. If my dh has not been there who knows what I would have done!!!
Look, OP. No-one but you understands your needs on that day better than you. If it's a case of you just wanted the father to spend time bonding with the newborn then I absolutely understand how important those first few hours are, but, as awful as it sounds (sorry dads) the most important person in the whole universe to that new baby is their mummy and there's no reason why the father can't catch up on that later in the day and the following days. If you felt like you really needed him around for you then I do feel that's different. What if he were the woman in the relationship and he'd just given birth instead? What the heck would he have done then?? I daresay this is a situation lots of women find themselves in! Blended families are not uncommon these days, and blended or not whenever a new sibling comes along you always have to tread carefully to avoid jealousy. I don't know, I guess there are ways to approach this without having to abandon a new mum and baby or make the step sibling feel pushed out!
I'm sorry you've had to deal with this now though, OP. I have terrible regrets and a little bit of lasting resentment over things that happened to me during those first few days and it can really spoil what should be a momentously happy occasion. Please try to find a way past this so you're not spending your time dwelling on it (easier said than done!) and I hope your oh is making it up to you too if he's been a bit of a twat about it!