And when people say your sex life will change, it doesn't always mean for the worse. Sometimes it's better! With the commitment you have made, sometimes it gives you the ability to really open up and really explore with your partner. You both need to take responsibility for keeping your sex life fresh and fulfilling.
Seriously, premarital counseling is important, as is counseling throughout your marriage at points of change. Before my first marriage, we didn't get it, because we thought we were invincible, but after some tragic things happened in our life, we found severe cracks appearing in our marriage. I we'd gotten counseling beforehand, we may have been better equipped to weather the storms.