Dear L.,
Well, for one thing, you are on the road to solving this problem already and you need to recognize it. You are looking for ways to change his social habits and you have a father figure that will help you too. There is a very good book on raising boys. It doesn't talk about girls, much, if any. I have given it to several friends and my daughter too. I can't remember the author or the title right this moment, but it will come to me and I will send it to you. If I can find my copy I can mail it to you.
The one thing that I can remember from the book that seemed so simple, yet magical. Spend a lot of quiet personal time with him. You and your husband can do this separately. He won't come out and talk about what is bothering him right away, but as you gain his confidence and he bonds even more closely with you , he will come out and talk over his worries with you both.
Also, I am so glad that you are looking at him as an individual and one that needs your guidance, as I said before. Since he is the oldest you can be sure that he knows that you have pride in him as the oldest child, and make sure that he is brought into the conversation about what the family is going to do and plans that are being made for anything from dinner to is it too cold for the younger ones to go outside? He will be surprised at first, then start to feel better about himself and be more responsible.
When he is upset, one parent needs to separate him from the group and spend time with him until he is calmed down, and do not fuss at him, he knows why he got separated from the others, be it at Grandma's house or the movie theater, wherever, just spend that time, and it will surprise you.
Also, remember, he loved his Dad very much, and now that father is no longer around. He hurts down deep into his insides, and probably thinks that he is the cause of what came between you two, maybe not. These are guesses, one never knows for sure what is in another person's heart, we can only suppose until they tell us.
You don't need any more than this to begin, and then you can learn more as time goes by, but it is of utmost importance to begin asap, and do not blame him or fuss at him, please. You can TELL him that his behavior is not acceptable in your family, or that he is hurting people, you know what to say. But no blaming. O.K.? O.K.
Let's see how am I going to get that book info to you? Maybe you can contact me and I will be looking for it.
Good Luck, remember you two are savig a precious life. C. N.