Sunflower0440,
Holy smokes, i am just overcome with some intense thoughts about your bf. His tendency to look at young girls sexually is very disturbing.
While it's nice that your bf is willing to stop going to X site, or whatever reassurance that you seek, I can't believe that he will be able to follow through. Pedophiles are nearly impossible to treat. They are extremely resistant to change.
You have a son together, so I'm sure that you have some love for him. I feel bad for telling you how hopeless and sick your fiance's behavior is. I really don't want to hurt or scare you. But having been SA'd myself, I feel that I can't warn you enough. Get out of the house now with your son and seriously limit visiting.
Not out of spite, but to protect yourselves from emotional damage. Kids pick up on things incredibly early ~ don't let the cycle go any further! P_L_E_A_S_E!!
Very gentle hugs and best wishes to you. I am so sorry.