The only thing sadder than someone obsessed with a person in a relationship, is the one who is obsessed with a person who isn't interested- and pines for them regardless of how the person rejects them
Now, let's not be naive and act like stringing people along never, ever happens. I mean it's very cruel when it does happen, but if that person is stringing you along then you just need to suck it up and get over the fact that they're not that into you and that's that. No amount of waiting around and biting at their ankles like an abandoned puppy is going to do you any good.
It's honestly kinda sad when you explain to someone that if they say they're not looking for/ready for a relationship, it's just a nice way of them saying they're not interested- the worst part is when they don't seem to care because they seriously think that if they wait around long enough and that if they're nice enough, the other person will come around. They probably won't.