Purchase the book 'we're having a tuesday. I found it great for my step-daughter. As well, reassure him that he is loved by both parents. Always keep a positive front with him and speak to his father in front of him, both reassuring him that everyone is happy, even living in different homes. Its tough, I know! Good luck!
When you say you see him each weekend and in the week does he get to stay with you and have long quality time with you ,he may be missing his Moms love and attention, any chance you could have him more, I feel its very important for a child to have equal time and possibly more with their Mom, it does sound as if he has some seperation issues so definatly some positive talk is good and make sure he has sports and games in his life , not dwelling on being lonely.... by himself.
Thank you very much for your comments - I will certainly purchase the book having read the reviews.
He does do sports and spends time with both myself and his father (although perhaps not enough time when it is just me and him - which I need to change) - he appears balanced in every respect apart from this when he really does lose the ability to see reason - he is bright and articulate but this is obviously a worry and I hate to see him getting so distressed,,, I dont want to put him into therapy if I can avoid it as I dont want him to think that he has a "problem"
Thanks again