If you've had a relationship break up it is natural to question everything about yourself and your relationship. Questioning is good because it helps us understand what went wrong, what went right and what we should or should not do in the future. It's a learning process which will absolutely make you a stronger more capable person; You will grow and mature so long as you do not draw the wrong conclusions.
I'll explain what I mean by that. Questioning is part of the healing process and as such is a natural and healthy thing to do but you must be careful that you do not make universal judgments on your relationship or yourself; Because a relationship did not work does not mean that you are a failure in anyway. It also does not mean that you are unworthy or that any future relationship will also end the same way.
Every modern convenience, every system of law, every healthcare practice and everything else you can think of that has been created by people has come about by trial and error. Humans learn through making mistakes; Do children see themselves as failures when they fall while learning to walk? Did Thomas Edison think of himself as a failure when it took him a thousand attempts to invent the electric light bulb? Each person who has ever succeeded at anything has taken set backs looked for what they have learned and gone on to triumph.
Now set backs can be painful, soul destroying and certainly not what we want in life but it does not mean failure. Look for the lesson and the seed of opportunity in your pain set back; You are free to pursue what ever it is that you want in life. If that is a good, loving and stable relationship then that is what you have to look forward to.
Certainly spend some time asking yourself and your relationship but then put it behind you. Your future lies ahead of you, not in the pain of the past. Adopt this winning attitude and you will find the happy loving relationship you deserve.