My boyfriend is nice, but has a dark side too

It is important to be in a relationship where you feel free to be yourself. The issues you raise are pertinent and need to be addressed if you are to continue with this relationship.
It seems as if your man is insecure. We all experience certain levels of insecurity, especially when we are in such intimate relationships, but what you mention about your guy is a bit extreme. If he has started behaving in this manner when you are still dating, how will he behave after you are married?
Be warned
Sometimes, some people become insecure because of past relationships. If in the past his girlfriend cheated on him or he has a friend or relative that was cheated on by his girlfriend then this may have formed his beliefs to the extent that he suspects that you could be cheating on him as well.
This could also be an early sign of a potentially abusive relationship. No matter how rosy a relationship begins, if one is careful and observant as you are, it is still possible to discern warning signs early enough. There is a possibility that your guy has some issues that could make it difficult for you to have a normal relationship. What you mention are tell-tale signs of a deeper issue and these are red flags that you cannot afford to ignore.
Call it off
So, what do you do? First, break off the relationship. Seek professional help so as to get healed psychologically and to rid yourself of any wrong beliefs you may have about yourself. You then need to assert yourself and refuse to be manipulated by him. If he reacts and throws tantrums, then that will be a confirmation that indeed he has a problem. Don’t be moved by that and don’t cheat yourself that it is you who is going to help him solve his problem. You are not a professional counselor to do so anyway. You will only become an enabler to his problem and thus not be of any help to him at all.
The writers are marriage and relationship coaches,a barnieachoki@gmail.com