The problem may be that your husband wants you to show that you regret sleeping with someone else besides him even though you weren't together it still hurt him because he still had strong feelings for you. It may be very important for the two of you to get Marriage counseling you both hurt each other very badly and now are finding it hard to let go of the past, when you both decided to get back together you should have been able to let go of the past and work towards the future and since neither of you took the time to talk about what you did to each other so that you could move on you just hid that resentment and let it build to this point. A counselor can both help you communicate better to each other how the other is feeling and how those indiscretions hurt your relationship. Your husband slept with a prostitute to try to hurt you but two wrong do not make a right. Before you leave make sure you have done everything you can to fight for your marriage before just walking away, especially for your child.
Your husband is trying to punish you for not being sorry for sleeping with that man and that is why he is withholding sex from you, you have to tell him how you feel about that and also tell him that if things do not change or if he doesn't at least make an effort to make the marriage work then you may leave. He has to know that you are at the end of your rope and also realize that he has to fulfill your needs and vice versa. A counselor can help you to move past this but it isn't going to happen overnight it is going to take some time to work through the issues and you both have to want to do the work. You may want to think about apologizing if he feels you hurt him even though you weren't together but he has some apologizing to do also because he put your life in jeopardy sleeping with a prostitute. Think about the counseling and talk to your husband about it and see what happens. There also has to be alot of compromise in the marriage also.