It sounds like he has a phobia for commitment, it all goes well until one day he thinks that things are getting too deep even if he initiated the pace of the relationship he starts to get scared and then just shuts down for almost no reason. Fear of making a commitment is common in alot of men. It shows a person's inability to take their dating relationships to the next level. The problem usually gets worse because of the fear of committing and ultimately affects the decision making as to whether to stay in the relationship or completely break up with their mate out of the blue. It's easier for a woman to commit and stay committed but some men are different they will commit to a certain extent but then when things seem to become overwhelming they shut down like they have an on off switch. He was okay with the commitment thing until he felt he was losing control of the situation and his feelings and then he got scared and that is the reason for the change of heart.
He can very easily get over his commitment phobia by first accepting it's natural to have fears and second thought about if the person he is dating is right for him or not. Secondly he has to understand that it is completely possible to love a woman and still have control of who he is and what he want, some men fear that the woman will change them. He has to take responsibility for knowing himself and what his mission in life is, and staying focus about what he wants while being in a relationship. While he wants to still be with you he isn't sure he is ready for the next big step and that is why he is backing off now and wants to start all over but it's up to you to tell him how you are feeling about the situation and also you have to know your level of patience and how long you are willing to wait for him to final be ready but judging from his past this is a repetitive behavior and it may end up being a never ending circle.
He may need to seek counseling to see why this behavior continues. The therapist or counselor needs to determine whether or not he truly is a commitment phobic or if there is some other personality disorder present. If it is determined that he has a commitment phobia, then the therapist and her client need to work on uncovering what triggered the problem. It could be something that happened during childhood or maybe a broken relationship where he was truly hurt could be the root of his behavior. Either way you need to figure out how much you are willing to take and how long you are willing to take.