There are so many harmful myths about how sex is supposed to happen and one of the worst is that it is supposed to be spontaneous. Most people never question the validity of the harmful social messages we've been brought up on because they pervade our atmosphere like the air we breathe. Once you gain some freedom and distance from messages like this, you can begin to approach sex with much more realistic attitudes and expectations.
People often get upset at the idea that they might need to plan sex. They remember when they started dating and sex "just happened." Yet, if you think about it, dating is essentially planning sex. By setting up a date, you are taking special time out to focus on the connection between the two of you. You dress up, fantasize about meeting each other, prepare and get excited. Dating sex isn't spontaneous sex; it's anticipated sex.
Once you have joined your life with someone else's, time together has many purposes. You might spend time together running errands or talking about money, kids and all the day-to-day logistics of life. Most couples stop carving out time together where the focus is on building and enhancing their sexual and emotional connection. When you live in a culture where there is a high level of shame surrounding sex, soon one or both of you will likely move sex to the bottom of your list of priorities. Just as you've made a commitment to each other, if you want your sex life to last, you need to make a commitment to consciously cultivate your sexual connection the same way you did when you were dating.
This means it's time to get over the sex-is-just supposed-to-happen myth and start setting special time aside so that you can spend the next couple of days anticipating your outfit, your outing, your seduction and all the hot sex you are going to have when your date night arrives.