<human>: Can you provide a brief rundown of the text in within 3 sentences?

Backstory: A relatively new friend of mine invited me out clubbing with her other friends. Late into the night, my friend left the scene but I carried on partying with her friends.      
        
Later in the night, I saw the [18-19?M] hold his girlfriend [18-19?F] up against the wall by her throat. She looked uncomfortable. Minutes later they were up against the same wall kissing.     
       
The entire situation made me feel uneasy, as I don't know these people outside of this one night, and because the obvious fact that he held her to a wall by her throat.      
      
I asked my friend this morning about the couple and she said he "is a bit abusive but says it's a joke. he's an odd one".      
       
Now this group is all between the ages of 18 and 19, and I am 21 and a lot bigger than this guy, but I'm very timid and not aggressive in the slightest. When I saw this though it really raised my hackles and I wanted to intervene but felt unable to as I hardly know these people.      
       
Next time I go out with them, if I see the same thing happen should I stop him? I know if I saw a random guy hold a random girls neck the way he did I would stop him?
<bot>: ! - Witnessed male of couple I hardly know abuse his GF I hardly know, made me uncomfortable, if I see it again, should I step in?