I have namechanged (even though I'm not a prolific poster) because I know AIBU, and I'm ashamed to be feeling this way. I'm hoping MN can talk a bit of sense into me. Apologies for long post.
My BF and I have known each other since school, been close for 15 years, she's one of my favourite people in the world. We've supported each other through a lot of things. She had her first baby, a little boy, in Sept. I am afraid I've started to feel resentful about how our relationship has changed since her DS was born 
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In the first few months, I was totally sympathetic to how much her life had changed, and tried to be both supportive and unobtrusive. Went to visit when invited, trying to make sure she knew I was always available with practical help without being demanding of her time etc., and completely happy to fit everything around her and her new DS. My problem is, I still feel like this is expected 9 months on, and I'm starting to get a bit fed up.
Her DS has routine which means she can't do anything after 6pm, including having people other than her and her DH in the house (as it is their family bonding time). I think this it lovely that they prioritise this, but must admit that it rules out almost all social activity, and is getting on my nerves now DS is 9 months old and not a tiny baby. My only opportunity to see them is weekend afternoons (I work FT), and with weekends being busy for both of us this means I've only seen her half a dozen times since DS arrived, always in or around their home.
I totally know, in this stage of her life, DS and DH come first, but I think what's upset me enough to post here is birthday plans. We are both 30 this year, and idly chatted lots in our 20s about having a big joint event. Obviously that couldn't happen in the way we'd fantasised when younger. She was unable to come to my birthday meal last month, as she can't be apart from DS in the evenings. Hers is in August, and plan is for a group of friends to get together in the park so 'we can all spend time with DS'.
Childish bit now - I want to say 'I'm not that fussed about time with DS, I want to hang out with you!'. I've been through a fair bit in the last 9 months (made redundant, splitting up with LTP), and I've really missed her - both as support and as someone to have fun with.
So... I know I'm being unreasonable, but as I don't have children, hoping you can show me some things from a parent's perspective, and help me to stop resenting a 9 month old baby