Just got engaged to my girlfriend of four years, last night she punched me in face over looking at porn because she'd "Had enough." What do I do?

Backstory: She's an awesome lady, and I'm certain that she is the love of my life, but last night, she walked in on me having some "me" time and hit me square in the face. She's only about 5'4" and 100lbs so it didn't do much damage, but I'm still a little concerned about the incident.

A few weeks ago, she told me that she was uncomfortable with the fact that I watched so much porn, and I promised that I would stop, but a man has his needs, you know? I wouldn't judge her if I walked in the house and she was watching porn or reading 50 Shades of Grey, so why would she get mad enough to hit me for one softcore video?

She's never been violent before and it's out of her nature to act like this, and like I said, she IS the love of my life. I don't want to lose her! Should I apologize for looking at porn and man up?