We know all relationships are unique, and the break-ups that can result from them are, well, even more individual (particularly when it gets bad). But there are also some long-standing truths behind...
Being dumped can bring up a lot of self-doubt. You could start thinking that you're too fat or too scrawny; that you talk too much, or you're too quiet. All of these things are possible, but more than likely, the reasons that you were dumped were about the other person and not you.
The zen master in me wants to put on a soothing voice and say that everything happens for a reason, that we learn from our pasts, and that pain can be a teacher. But let's talk instead about the ways of doing it with class; ways that make it hurt less and leave the door open to friendship. Maybe not right away, but eventually.
If one or more deal breakers are present in your relationship, you'll have to see whether it's possible for you partner to stop what they're doing immediately. There's no point in waiting for them to change. You've already been tolerating the intolerable.