Hi C.~
My oldest son is now 18 (will be 19 in June). When he was around 14 or 15 he really started to pull away. I asked some of my mom friends why and what I could do. I was told that boys need to pull away from their mom, to feel independent, and to start to become a man. This really does make a lot of sense. All I could do was just watch him pull away and hope that he would soon see that he needed me as much as I needed him. A couple of years went by with him being distant, but eventually he started to grow near to me again, and this time it was different because he had changed some, seeming more mature and non-chalant(sp), but I was definitely back in the picture again, getting hugs, watching movies, hangin' out, talking.
Your son probably doesn't want to hang out with the girls because he wants to start to become a man. He needs his space to figure out who he is apart from you. And he can only do that if he separates himself from you for awhile. I know this is hard, I cried because I missed 'my bubba'.
I hope the best for you, when times get hard, lean on other mom's that are willing. If we all worked together as a community, things would be a lot better, and we wouldn't feel so alone in our situations all the time. God bless you!
A little tidbit about me:
I am 37, my kids are 18, 11, 9 and 4. The older 2 boys, younger 2 girls.