Everything is sailing along just fine. You really like him. Maybe you're even in love with him. He's very attractive. You get along well with his family. You two get along great, you laugh and hangout and you have great conversations. Then one day, he doesn't call. You call him, no big deal. He doesn't call you back. When you do get him on the phone, he may seem friendly and tell you he'll call you back, but never does. This goes on for about a week when you finally realize that this is his way of breaking up with you: suddenly and with no warning.
Unfortunately, this scenario is common, and what's even more mystifying is that age is not a factor. The fact is it happened to you and it can be shocking and devastating. You need to get through this.
Realize that he is not going to call or come over. The sooner you come to this realization, the better.
Know that there is a reason for this, and you probably will never find out what it is. There's no such thing as "he broke up with me for no reason." He has a reason for doing this, and it's probably stupid and misguided, and most likely has nothing to do with you.
Resist all temptation to call or write him, go to his place or job, or call his family and friends. Do not do this. True, you're going to jump every time your phone or doorbell rings, or hold your breath every time you go into your email, but you will make no moves towards him. Ever.
Pour all of your feelings into a journal. If you feel like you want to write him, write a letter, but do not mail it! Writing can be very therapeutic and if you've never done so, now is the perfect time. One woman used an entire 8 x 11 inch pack of paper to vent her feelings.
Lean on good friends, every day if you have to. Hopefully, you have someone whom you can confide in, vent to, and someone who'll even want to smash his car lights out for you (don't do it-jail isn't worth it). Being able to talk to a friend at this time is a very critical part of moving on.
Get out of the house. Do not stay in. Find something fun to do that will take your mind off of things. It's even better if you can be around other men. Don't fall into the "I don't want to be around anyone else right now" mode. You need interaction. Just socialize; it's probably best that you don't give your number out for dating purposes now, but you need involvement.
Know that to really get over a person takes time, especially when the break-up came in such a cruel, sudden and cowardly way. But if you follow these steps, you should have relief at least within a month. Relief is what you're looking right now.