The main problem with giving clear answers to your questions might be in shear complexity. In the first place you`ve done nothing, and are doing nothing wrong, unless in trying to create situations for your boyfriend to rescue you from, as previously suggested to? Optimal rescue is not always an option, most of the damage often already being done. To retaliate is not a rescue. The best option for rescue in this case was for your boyfriend to have apologised to you on their behalf, and then to have had nothing to do with them until such time as they should apologise to you to your complete satisfaction; which would doubtless be never. He would have rescued you, or tried to, somehow, certainly if his relationship with you had been more vital than that with them, but perhaps only then if there was already the real threat, real to him, in place of your loss - You weren`t at the same time trying to ask whether he`s a nice guy? It`s natural to want a boyfriend to stick-up for you, but be mindful as to when you expect it, and how.
Their antics might be explained, as it appears to be gang cult behaviourism - you don`t need to be a member of a gang to display it though. Could be they were establishing/reinforcing an order of allegiance, for only then does it make any clear sense, apart from revenge? - Demonstrating that they are his first mates and not you - Nasty! Another example would be, you arrive at a hostel with other girls to begin a course. Some of them go upstairs and start throwing water down on others of you from the windows. This is to establish a pecking order: These people sound a bit primitive if this is the case, and the more reason to avoid them.
You seem to be with the wrong crowd(?)