The modern lifestyle can kill intimacy in a marriage, if not well taken care of. Couples find themselves dealing with different schedules and career demands they gradually drift apart. Couples put the needs of everyone else - including those of their careers and their children - before those of their spouses then get shocked when the relationship breaks down.
The husband-wife unit should be the most important relationship in one’s life. Nurture it. Give it the attention it needs to thrive. Don't allow anything or anyone to drive a wedge between the two of you; the extended family, career, friends, hobbies, volunteering or anything else. Once you allow your intimate relationship to crumble, it will negatively affect all other areas of your life.