How do you keep your relationship from breaking with young children?

I'm not a mother, yet. In a few years I would love to start trying but there's one thing I fear, losing what me and him have; love, respect and honesty. I've seen many people who look so happy but many where it seems one parents has been pushed to the side and sex, communication and respect are all lost. They seemed to be so happy before children though.

It really worries me that we will lose each other in the mist of life; work, kids and etc. How do you manage to stay focused on your significant other with children?