Insanity is doing the same thing over and over again and expecting different results

You'd think I'd know that. But I swear I just keep setting myself up for disappointment over and over again. You'd think that I'd know by now that this person is highly unlikely to follow through on things they say they'll do. Or at least things they agree to do in regards to me. Yet I continue to keep trying. Why can't I just let some things alone when I know I'll just be disappointed yet again? Must I continue to give people the benefit off the doubt just to have it blow up in my face over and over again? Some days I don't know why I do such things. Sometimes I think that it would be easier if I didn't care about people or things at all. Because when they keep disappointing you over and over again, it's the worst feeling ever. I just wish that I could convince myself to stop trying. But I've always been a hoper and a dreamer. I've always expected people to be the best they can, without forcing them to be. Yet I can't seem to make myself stop hoping they will rise up to the challenge. As often as I keep having glaring facts and such that I should give up on certain things, I can't seem to let myself do so. How do you give up on a someone? Even though they let you down all the time. Even though at this point, you should have given up on them ages ago because anyone else in this situation would have. How do you stop trying to get their approval when they hardly spared you a thought in a good long while? Or at least, you don't think they have because wouldn't they have told you? Or tried to get in contact with you rather than you being the only one trying all the time.
How do you have a maintain a good relationship with someone when it feels like they've stopped trying? Or that they think it'll still be exactly the same as it was the last time they were there. Don't people realize that someone can only try so hard for so long before they just can't keep trying? And how do you tell that person exactly how you're feeling when it seems all things you've been trying to say falls on deaf ears or goes unanswered?
Some days I just don't know any more.