I got a new nephew - and a whole big set of issues

My sister gave birth to a beautiful baby boy, Ethan, in the early hours of yesterday morning. This was after what felt like the longest pregnancy ever and definitely one of the longest stop/ start labours ever (although in fairness, once it really did kick off, it really kicked off)
I met Ethan yesterday morning - looking very much like his big cousin Joseph did at the same age. All 6lbs something on him, with blonde hair and chicken legs.
My sister is besotted. (Sore, ya know, but besotted). She doesn't want to put him down and can't say as I blame her - he's pretty damn cute.
But a little part of my heart broke yesterday because I thought I was over my birth experience and my post natal experience. I saw her cuddle him, and hug him and thought back to the 24 hours after Joseph was born. I barely held him. I was too damn tired.
I knew he was my baby and I knew I would bust the arse of anyone who tried to hurt him, but I didn't passionately feel that mother love. I didn't marvel at his ears, and his fingers and his long feet. I didn't spend my day smelling his head and kissing him. I fed him, and changed him and saw to his needs.
That made me so very sad - to see her like that yesterday. Happy for her, of course, but sad for me because I'll never get that back with Joseph now and while I love him and he loves me and we are close as two close things in a close place I'll never have the memory of marvelling over a newborn him.
That kind of really, really sucks.