Do all relationships suffer after a baby?

No, all relationships don’t suffer. It sounds to me like instead of working together to support each other, you are competing: who has it better/worse, who does more of value etc.

Resentment will kill your relationship if you let it continue. It is very common in the early months of pp but not so common IME after 16 months. Are you a SAHM by any chance?

Sit down, make a list of everything that has to be done, next to this write down the name of the person who currently does it. Make a note also of how much time each person gets to themselves each week. Then you can both see who is right/wrong and what needs to change to achieve equality in your parenting relationship.

But yes, it is quite commonplace for this to happen. A baby creates a massive amount of extra work, more than people can imagine before the baby is born. What happens then is that both parties feel like they must be shouldering most of the burden just because it's so much, but often it's the case that it's just soooo much that both parties have a lot on their shoulders.

Once you have the list of all the jobs that need to de done and who does them you can look to see if any of those jobs can be done by someone else (can you get some childcare/a cleaner/a mother's help/a dog walker/use an ironing service etc etc) or reduced (can you wash towels/dust/shop/clean the car/mow the grass less frequently/more efficiently).