I agree with the above posts. Adult kids feel the need to exert their independence and often feel they no longer need us. Give him his space and get on with your life, once he realizes that mom's nowhere to be seen, he will come looking for you. The pendulum will swing too far in the direction of his independence, but evenutually it will find a happy medium. Live for yourself, do things you enjoy, don't stand for any disrespect from him either. He knows you love him, but is a little too sure of it, back off and let him wonder a little, it will be good for him.
The best advise I can give is to get counselling.... Lily
All you can do is let your son know that you love him. Then, live your life. Get involved in activities outside the home so you aren't obsessing over your son. One day he'll probably come around, but until then, you must go on with your life. Kids can be fickle and emotional, even when they have reached adulthood. One day he'll probably want to reach out to you, just make sure he knows your door is always open then let him be.