Always always always have a 'ducks in the row ' mindset as a woman.
Make sure you're married as you are so much more financially vulnerable after having a child.
We were together 11 years when we had our eldest but we'd been through 5 years of miscarriages and fertility issues by then. We'd run a business, suffered significant family bereavements, health issues and various barriers so we knew we could work together and that we responded to adversity by coming together rather than falling apart.
What I wasn't prepared for was how much experience I have/had with children being from a big family, lots of babysitting, nannying for cousins in holidays etc while he first held a baby when my nephew was born 10 years ago. Never have I seen him more practically useless. He struggles after our first who has health issues and later SEN, lots of hospital stays etc and the routine changes really knocked him sideways (origin of SEN genetically very likely from my lovely, almost definitely autistic husband)
However we're 18 years in now, 2 kids, can laugh at all the ridiculous indignities of parenting. Still love each other, definitely less sex but still sex. Less spontaneity with holidays and going out on a whim but thanks to my mil doing a few weekends a year we have tickets to 3 gigs this year and even eldest can now be babysat by a close trained family member.
I don't know that longevity in a relationship makes a huge difference but I know we were very used to each other and had seen each other in many scenarios before the babies. I love that man! He does the dishwasher every night, we do half the bedtimes and we both work so we're pretty even in terms of responsibility now.
We struggled more when no one slept and I was breastfeeding and he was the main breadwinner, it was just so foreign to not relate so well toe ach others days.