Dreams are expressions of our feelings about our waking life interests and concerns. Unfamiliar people who play a big role in our dreams are often symbolic. The trick is to ID "him" or "her." Most often your gut impression is the right one because it "feels" right. It's not unlike sensing in a dream that you are in your childhood house, but you doubt it because it doesn't look exactly the same. Our minds use "creative license" in dream creation. While those differences often contribute to its meaning, don't allow variations in physical appearance or behavior to distract you from the symbol's true identity, especially if you think or feel that it's someone or something you know. That being said, it's a good idea to test your gut impression against the waking life background of your dream, as well as other clues IN the dream. In your dream, the setting is social and includes other friends of yours, so it makes sense that the dream relates to your social life, as opposed to something going on in the classroom or at home.
As for whether or not this guy really is as possessive, jealous and threatening in waking life as he was in your dream, your dream is making an emotional point. Dreams do not lie when it comes to our feelings. How you feel IN the dream is how you are feeling about its subject in your waking life. At the time of the dream, you were feeling scared and concerned that he or someone else may come after you or your friends in retaliation. The main message of the dream is that you are scared about what he might do. It doesn't mean that he will do anything. If he doesn't have a history of behaving that way, odds are he won't.
Scary dreams alert us to a fear we have about something going on in our life. It doesn't mean that something bad is definitely going to happen, but it is a feeling or sign post that we should not ignore. Just remain sensitive and alert. Once you have identified the cause of the fear, take appropriate steps in waking life to protect yourself. Feelings do change and your dreams will reflect that.
Good luck!