It is permissible to engage in coitus interruptus and to use a condom if the wife gives her permission for that. For more, see the detailed answer.

Sexual fantasies are thoughts that occur to most people, especially the youth, but they vary from one person to another with regard to their type, strength and effect. If a person imagines haram things that came to his mind unbidden, there is no blame or sin on him, rather he has to ward them off as much as he can.