You can never know.

I’m a proponent of having a long relationship before major decisions. I’m not saying people who have kids in their 20’s are doomed, but I believe that having a longstanding strong relationship prior to having kids is key. The fear is still there, but the knowledge of how your partner reacts to strife and hardship, goes a long way compared to NOT knowing.

As to changes, of course you’ll change. Parenting a newborn is different than parenting a toddler is different than parenting a tween, etc, etc, etc. Embrace the change. Embrace the challenge. Don’t have kids expecting it to be easy.