I'm meeting someone at a basketball game tonight and all of my friends are busy or sick, will I look like a weirdo or a loner if I meet him alone?

Well it depends on the person. But most people would say no if they were in that situation. The person is probably happy that you are meeting them so they wouldn't really care whether or not you brought someone with you. And if they asked if someone was with you, it's most likely out of courtesy instead of trying to bash on you. Honestly, most people don't think that far when they see you alone (unless they see you alone all the time) so you have nothing to worry about. And if he happens to think that, then he's probably an inconsiderate and assuming person to begin with.