Please Help! Developing Aggression

hi there, one of the problems you have is his age. It is the 'teenage' months that I found my dog was very willing to see how far she could go with other dogs and was very rude when approaching other dogs. So on that, I would say to be patient and when he is over 1 year old he should be a lot more polite.
But, you can do things now. What worked for me was to develop a really good recall. Is your dog off line? I found that my dog could quickly greet a dog, and then almost instantly she would start a fight. I worked really hard on her saying a quick hello then she must come to me and sit down. After a moment or two I found that she had sussed out the other dog(seperated) and then I could let her go and play. I needed to do this on a line at first, but now she can meet, come to me, sit, then wait for the signal to play.
When the dog is on the line, don´t fall for the trick that the dog lunges forward and greets the other dog first. Work with the other owner that you approach, ask the dogs to sit seperate, and then the owners talk. After a while the dogs may sniff or play off line. It is not OK for your dog to drag you over to another dog and then be aggressive. Make him wait, and if his behaviour is not ok DON`T RUN AWAY, but make him sit, ignore him, and carry on your conversation. This should show him that you are the boss, and only when he is relaxed does he get to meet another dog. I found I had very few problems when my dog had a moment to watch the other dog. She seemed not very good at that first contact. But as I said, it is also an age thing, so it´s great that you are thinking about this problem, but don´t worry too much. Whatever you do, don´t stop all contact with other dogs. Find an older friend dog who will discipline your dog in return when it´s too much, and other friendly young dogs to play with.
I stopped ALL rough housing with my dog as I have young children and it just didn´t work. Your dog is still a puppy, however he needs to roll around with other dogs. It is possible that your boyfriend is too rough with him and somehow has hurt him. He sounds like he does not fully trust your friend......When humans wrestle with dogs we should always be aware of when a dog says ' that hurts' or 'too much, stop' and if we ignore these signals, your dog will ignore them in others too. Wrestling with a dog should be like with a child. A gentle tickle session and rumpy on the floor for fun....not a 'toughening up' session to make him into a 'tough-dog'. Men sometimes enjoy training and the prestige and power this has. Maybe your boyfriend could work on a special 'trick' with your dog ( play dead is fun, as is crawling forwards!)
Good luck,
Annie