K.L.
From the information you have given, there really are a number of possibilities. I agree with one response you received that you might want to consider bipolar disorder. Narcisistic behavior tends to be more predictable and constant, although a narcisist will not hesitate to use shock and surprise to manipulate someone. The difference is that a narcisits is more likely to plan and plot the surprise where the person with bipolar disorder is more suddenly overwhelmed with mood swings. For example, with bipolar you might have someone who is always blaming themselves for everything and then they are suddenly blaming everyone and everything else for everything. The narcisist, if clever, will always find a way to blame others.
But there are other fine differences in mental disorders to consider as well. If you want to understand how to recognize sociopathic behaviors in order to make sure you avoid such relationships, you might want to read The Sociopath Next Door, by Martha Stout. It is an eye opener!
The caution I would offer you is to not leap to the tendency to diagose such conditions just from reading about the symptoms of a disorder or two. There are very specific differences in the physiology of neurological functions related to each disorder. What you do want to diagnose is whether or not someone is capable of supporting a relationship that has the potential to evolve before allowing yourself to invest anything precious into that relationship. You want to know if they lie, how they respond under stress, if you see them acting oppressively, selfishly, or childishly toward anyone, etc. Know the strengths of character you are looking for. Can he consult objectively and patiently over serious matters? Can he use humor constructively to smooth out the 'small stuff'? People often look for someone with similar interests. The fact is that many happy couples may share common or complimentary standards, but may also have very different tastes and hobbies. Many people marry the person they like to play tennis with or look for the guy who likes to watch chick-flicks. It seems more reasonable to look for the guy you would like to stay home with and with whom you can face lifes challenges. You can always play tennis or go to the movies with your girlfriends. Women who look for men who become their 'everything' often find controling men who really want to be their 'everthing'. The movie, Runaway Bride, makes this point.
Don't think I am aiming judgment at you. I don't know nearly enough to have a valid opinion. These are just general tendencies many women experience and are good to think about before seeking another relationship.
The one thought I would like to leave you with is that it is important to look back on that relationship in order to learn what you need to know about yourself and how to not be vulnerable to such things in future. But, don't keep looking back to diagnose him or believe that you can heal him by subjecting yourself to an unpredictable and abusive relationship. He needs to find the therapy that might help him before he invites anyone to share his world with him. If I were in your place, that would be my only message to him. That, I have learned, is what you do when you love someone and you love yourself. This is the best way to protect the dignity of everyone involved.
If you feel close enough to his child to take an extra step, you might ask to speak with the counselor at the child's school so that extra awareness and possible support might be given via appropriate channels. Just make sure they know you are coming to them only on behalf of the child in order to give them information that might be helpful to the child's teachers and because you are concerned about the child's well being. Schools have to deal with warring couples who bring their fights to their children's campus and will try to avoid being used as an agent of either party. Be careful to only give them information that is related to the child and do not disclose anything personal about your relationship with the father.
Anway, these are my rambling thoughts after reading your message. Hope some of them are helpful to your process.