Having kids will end your marriage
Unless your relationship is ROCK solid before you have kids, forget about it. Boom, you're done BrAngelina.
The irony of having kids is that some couples believe it will save their marriage and somehow bring them closer together. Make no mistake, the joy of children will shine a bright light on the dark corners of your relationship, and will expose and magnify each and every character flaw you both possess.
If your union of souls is fated to be doomed, then a child is the nail in the coffin. If, however, there's a glimmer of hope, you'll need to do these things to keep your heads above water:
1. Have a sense of humour - If there is only one thing that you can do from this list. This is it. Both of you are going to have baby brain, you're going to be tired (nay, EXHAUSTED), hungry, and short on patience and hygiene but long on stress levels. If you can get over yourself for a minute when shit hits the fan, and just laugh it off (whether you're being a donut head or your partner hooped the pooch), there might be hope for you yet.
2. Don't keep score - This goes for a relationship without baby too. If you keep score about who does what chores how often, it is sure to spark an argument. Add a child to the mix (in daddy/mommy spousal situations, gentlemen, you don't stand a chance of winning a score-keeping contest, trust me), and now you have a situation where both parties are emotionally invested in that score, which can make for a pretty explosive debate. Instead, if you see something that needs to be done, just do it. Nobody WANTS to do it, but it needs to be done, and letting it sit around just creates a bigger mental load for everyone.
3. A little thank you goes a long way - If your partner does ANYTHING for you, your baby or your family unit, thank them. Being a parent is a thankless job. Babies are little black holes of greed and have a way making one feel exceptionally underappreciated. So any appreciation you can offer your fellow adult, no matter how small, is registered consciously or subconsciously by your better half. An interesting phenomenon occurs within your partner as well; psychological studies show that when we do someone a favour, we tend to like them more. And so by you thanking them, and subtly indicating that they did you a favour, you increase their appreciation for you. Win/win!
4. Communication is king - This was and is the hardest one for me. I'm not a sharer, to a fault. Not only does it do you good to talk about your hopes, dreams, frustrations, and motivations, keeping this from boiling over after stewing about them on the inside for too long, but it gives your partner a chance to share what they are feeling, and keeps you connected to one another. When you have a baby or toddler, it's all about the kid all the time. Take some time to talk like an adult (instead of "did you make a poopoo in your diaper?), to an adult, about adult things. You were people before you were parents, and a couple before you were mom and dad, try to take a little bit of time each day to chat about something that doesn't pertain to your kids.
5. Ask for help - I have twins. We asked for nothing from anyone. A few offered their assistance, knowledge, love, and hand-me-downs, for which we are eternally grateful, but for the most part, my wife and I have done it ourselves. And it almost destroyed us. There were a lot of tough days where I wasn't sure I would survive. My wife handled it much more gracefully, for the most part, but it's hard to be sleep-deprived, wake up tired, take care of business, and commit all other waking hours to your infant. For those of you still in the midst of this haze, it gets better at around 18 months, you can do this. But it's hard, and actual real help would have gone a long way, in the first 6 months in particular. And that's not blame those who didn't help, chances are they didn't know you needed it or what you needed, but my advice is not to be too proud. We all need help from time to time in our lives, and this is one time where you will enjoy your kids much more if you have supports ready to go.
6. You both need to be the bad guy - This is to the benefit of your relationship as well as the development of your kid(s). Nobody wants to make our kids angry, sad, say they hate us and wish we would die, etc., but if only one parent lays down the law, it will create a rift and resentment from your partner (the "tough one") and your kids will pit you against one another going forward. Kids need boundaries, and they need to hear a consistent message from their parental unit. United we stand or divided we fall.