Most Helpful Guy
I can answer this question for you. The most foolish thing to do after a break-up would be going for a rebound relationship. These rebounds are almost always guaranteed to fail. It is likely to leave you with a lot of bitterness which could take forever to heal, and it would also be totally unfair for your partner because he might have expected a long term relationship but it was bound to fail since it was a rebound relationship. Hence, please refrain from rebounds relationships at all costs, because such relationships are a sure fire recipe for disaster. Give yourself time to recuperate.
Having said that, there are lots of thing which you CAN do, to deal with your pain. Getting drowned in music would be a good option. It is often said that music has charms to soothe a savage beast, so it can obviously heal the pains of a hurt 21 year old girl. I'd suggest you refrain from listening to romantic music or songs with lyrics related to love, because that might bring memories flooding back. This would actually nullify the purpose of you listening to music. But this doesn't happen with some people, so you're the best judge to decide if you're fine with listening to romantic music in your situation, although I wouldn't recommend you to take that risk.
The next thing you could try, is to start playing video games. And no, I'm not referring to silly Facebook games like Farmville and Cityville. There are games which are totally immersive, and provide you with long hours of entertainment. Also, video games are excellent stress busters. I suggest you play games with high octane, fast and frenzied action, because that adrenaline rush is likely to numb your mind and make your forget your painful breakup to a certain extent.
The next thing I'd suggest is to hang out with your female friends quite often, and have fun with them. I'm specifically saying 'female' friends because most males are jerks when it comes to things like breakups, and what they say might actually intensify your pain. And since you're single and in pain now, guys might use your vulnerability to start a relationship with you, which would again be a rebound for you. Also, girls are usually quite understanding in such matters, and offer you their shoulder to cry on when you're low. But there is a class of girls who actually enjoy seeing other girls suffer due to jealousy, so you'd better stay away from such girls.
Finally, I'd suggest you involve yourself in some physical activity on a regular basis. Swimming would be the best option, because it REALLY de-stresses and refreshes you very effectively. If you don't know how to swim, then other physical activities can also provide almost equal benefits.
I hope I have helped you a little bit at least. I may be a newbie on this site, but I deal with relationship issues on other sites such as Yahoo Answers. Feel free to contact me if you need further assistance. And please remember, strictly NO rebound! Take care, and have fun! Cheers! :)