Because you’re a parent, you have to put your feelings on the back burner and do what’s right for your son. 😉 Since you decided to get married, I think you should try to make it work for the sake of your son. It sounds like he’s been through the divorce you probably had with his father, and now, there could be another with his step-father, and the boy is only eight. 😳 Put him first. You can’t honor every feeling you have — instead, you have to honor your commitments and your responsibility. This is an important lesson about character that your son will be learning from you.
So, first, break off contact with the guy you cheated on your husband with. Until he’s out of the picture, it’s going to be very difficult to focus on your marriage, and for your husband to feel like you’re really committed. When you make things right with your husband, then he will probably feel more generous towards your son. 🙂 You’ve got to put yourself in his shoes — he’s hurt that you cheated on him, and hurt future that you continue to keep your ex around. This isn’t going to foster his best behavior, to say the least.
See if you can make the marriage work for the sake of your son, at the very least. It won’t have a fighting chance unless you let go of your ex. 😉