Boyfriend's seemingly strange attachment to adult son

I have been dating someone for 3 months. We hit it off immediately and were spending all of our free time together. On December 10, his 21 year old son came into town for a month. I didn't think things would change very much (I have small children and only have 8 days per month to see him anyway.), but they did. Well, he would not leave his son for a minute even though his son was also visiting his grandmother, aunts, uncles and his half sister. I only saw him alone for two times while his son was here and one of those times was only for 1.5 hours. Each time he said how guilty he felt for leaving the son. He did include me to do things with the son, however. His son left yesterday and now he is completely devestated and depressed even though he will see him again next month.

Okay, here are the circumstances. He has three children. His wife left him for another man about 17 years ago. A few years later he agreed to let her take the boys out of state. The boys are now 18 and 21. (He has a 16 year old daughter from another relationship who lives close to him.)

Here's why I think the attachment to the oldest is strange. He favors him more than the other children--a lot more. He spent 3 times as much on the 21 year old for Christmas than he did the 18 year old and even less on his daughter. The daughter is suffering from what could be anemia or something worse, but he was so distracted by 21 year olds visit, he only called her once to check on her, didn't get through and as far as I know didn't call her back.

My question is do you think this man's attachment to his adult son is strange/abnormal and why? I need to understand this if I'm going to keep dating him.

Thanks.

Hi, sbasso! If he's spending much more time with him than with his other kids and is even neglecting the others, it does sound strange to me. How does his son feel about this? Does he seem uncomfortable with all the attention his father is giving him?
I'm not a professional, but maybe your boyfriend is emotionally dependent on his eldest son or something like that. Does he do anything else that seems strange?