When you like someone and ask them out but find out that they don't feel the same way, it can be really difficult to deal with. However, just because one person doesn't share your feelings, doesn't mean that you have to give up on dating. Instead, use this opportunity as a steppingstone to get where you want to be.
Maybe, the other person isn't ready for a relationship. Maybe, he or she is taken, or maybe, he or she is just a friend. Either way, maybe there is a reason that the two of you didn't end up together. Maybe, there is someone out there that will connect with you on a deeper level than the person that you originally asked out.
If a person decides that he or she doesn't want to date you, try to be cordial. If you can establish a friendship with him or her, then do so. You might find out that he or she makes an excellent friend. Respect his or her boundaries and allow yourself to move forward. Just because one person doesn't share your feelings doesn't mean that it is the end all.
You might find yourself in a situation later down the road where you meet the person that you decide to spend the rest of your life with, and you might find that if you had continued to pursue the person that wasn't interested, you may have risked a beautiful friendship and a chance to find the one that you eventually were going to end up with.