I think you made the right decision for you, and for the reasons you stated. If you had gotten into it with that guy, he might have even grabbed your weapon and turned it on you. Never get within striking distance with an adversary when you are armed. - Mike
+1 Like others have stated, you'll never know unless you're in the situation and feel the energy of the moment. I think you made the right decision for you at the moment it happened. BTW, was your daughter there? That certainly makes a huge difference in my response if I was in the company of my family.
I probably would have stayed 15-20 ft away and asked the girl if she's ok. Like others have stated, most women in "love" probably would attack you if you tried to offer a lending hand.