When you aren't emotionally available to your partner, you're withholding the intimate details of your life: the very opposite of what you should be doing to build a more intimate connection. What comes along with that is a decreased feeling of appreciation and value -- that specialness that comes along with an intimate relationship -- on your partner's behalf. After a while, that can have detrimental effects not only on emotional intimacy but also on sexual intimacy as well.
Make it a priority to share the daily details of your life with your partner, such as what's going on in your work life, as well as your secrets. Sharing the feelings and dreams that are unique to you shows your vulnerability as well as how much you trust your partner to accept the real you.