Confused

Amanda
My fiance and I found out we r pregnant, I am 6 weeks along. I have 2 kids from a previous relationship and he has 4. My son is 15 and he is disrespectful and lies alot. My fiance has now decided that because my son disrespects him that he is moving out. He says he loves me and wants to b with me still he just can't live with me because of the disrespect from my son. I don't want him to leave but my kids will always b the most important. No man will ever come before my kids ! How can I fix things with my son and him ? Talking to my son isn't working