As others say, the 'firsts' don't matter a jot. The first time YOU see your baby crawl or say a word will feel special. The firsts thing is sometimes used as an emotional thing to make mothers feel they can't possibly leave their child for a moment. thank you for saying this Babbitywabbit it's just what I needed to hear.
OP I left DD at 5mo (shared parental leave so she's with my husband until she's 11mo) and it felt absolutely gutting. In the run-up to the end of my maternity leave, I was really dreading it.
However when it actually came to pass, it was okay, it wasn't nearly as bad as I'd anticipated.
For the first couple of weeks I felt the freedom of commuting and working, it was amazing to have two hands free, I hadn't had that for five months. Work felt like a bit of a novelty.
It got a bit harder for a while after that, I could see her growing and developing, babbling nearly-words, sitting on her own, crawling, weaning... and there is a part of me that feels like I'm missing out.
But all-in-all, it's for the greater good, DD is well cared for and loved, I need to work both financially and psychologically, it has really helped me feel like myself again.
I miss DD a LOT, but she hasn't forgotten me, I come home and she's all smiles, and no one can make her laugh like I can. There is an unbreakable bond there.