I think someone might be obsessed with me. I have already made it clear that I do not like them in the same way. What can I do to get them to stop?

I would try to ignore them to the best of your ability.  Many times if you do not give them the attention they crave, they will go away.  If they are obessed with your and stalking you, start to document it.  You might want to think about getting a restraining order.