how do you teach an old dog new tricks?

have you ever noticed that the things people want the most in life are unavailable to them, no matter how much explaining someone can do, i still will never understand. see here is this girl who loves this boy, and the boy doesn't love her like that, and just drags her ass around, but when the girl finally finds a boy, the old one wants her so bad. starts acting like the perfect catch. seems pretty fucking wonderful if you ask me. hahahahhaa, but really it's a funny situaiton, cause the girl obviously still loves the boy but she knows when she makes herself available, he'll go back to his old ways. so how do you teach an old dog new tricks??? you don't, you settle for the way things are and build a fucking stupid shitty as bridge and get the fuck over it, cause people don't change. especially if they are not willing too. so what should the girl do, well we know that she will still pine for the old "dog" but maybe, just maybe she needs to let him go, and never look back. cause once you do, theres no looking foward again.