..if you look for other people to make you feel comfortable with an idea and you need their approval or disapproval you will soon find out that there is as many opinions as people you ask. Whose advice are you going to take? You're simply gonna go crazy and confused. Do whatever seems right for you. If you feel you need a one night stand - go for it. You are not the first and you wont be the last. If you find out afterwards it's not what you wanted- don't do it again and you got that idea out of your head. But as other people have said before...be careful if it is really what you want or else you will end up hurt or hurting someone else. Sex is a delicate subject and should be treated like it. Even in a one night stand there can be mutual respect and a genuinly positive feeling for each other. It is your choice if you turn it into something cheap and nasty or if you are having a good time with someone you respect but are not interested in going the full way (relationship and all).
Also, I would maybe think about more why you seem to be attracted to people whom you know won't be interested (unconsciously). Did you grow up with a vacant father who was hard to approach and absent or absent-minded (that's just out of pure interest)? Do you feel you actually deserve a really good partner? Or do you feel inside you have to perform to make them stay or like you? I'm just speculating..sorry