Why am I so unlucky.......?

No, you're definitely not the most unlucky person alive. How can you be sure no one has truly loved you? Maybe by learning some social skills you can acquire more friends. Within those friends, try to get a variety of men and women (so maybe one day you can date one of the women). Instead of worrying about different women (which I'm glad you DO have a heart though), worry about your career, your vacation, your self-improvement. If she gets used for sex...well, that's too bad for her. You should tell her firmly but reasonably that you are worried about her getting hurt. If she doesn't believe you, or does not appreciate it, then don't persist. You should think about the things you TRULY want before you can say that you can't get them. Good luck.