It depends. If you are going to constantly argue around him and there's going to be constant tension, it's best that you separate. While growing up, my mom constantly said to others "When Mara grows up I can finally leave and be happy." I always felt guilty about their staying together and it was very hard to live with. If, on the other hand, you can live in amiable conditions then it would be better for him to stay with both parrents. Depends on your situation. Just think of your son first.