I am very saddened by this thread.
Lots of people have very rigid ideas about what an event like this means, but it doesn't need to mean any of those things. It is something that happened and analysing why it happened, the meaning of it happening and what it means about the OP as a person or her DP as a person won't move this forward in good ways.
I hit my husband once. It was a freak thing. We were standing outside a library trying to get my screaming baby into a sling on top of me. Night was falling. To the right hand side of us, there was a gang of youths who I was quite scared of. Dh came at me quickly and I just lashed out at him and hit him.
There was no "real" threat to me, but I was in "threat mode" and also, unbenownst to myself at that time, acting as many survivors of childhood physical, sexual and emotional abuse do... it triggered a primitive part of my brain which took action without my thinking brain, without any sort of knowing. I was also (again unknown at this time) in the early stages of pregnancy and pregnancy and the postpartum period are times when we are more likely to experience hormonal shifts that can activate the threat system in ways that are not in line with our values or general actions in the world.
Six years on and all is fine. I was diagnosed with a perinatal anxiety disorder within two months of this, got medication, a LOT of therapy and learned how to regulate my emotions using Mindfulness and Acceptance strategies. The work is ongoing and probably will be for the rest of my life but that event remained a one-off that was the catalyst to many changes for the better in our lives.
The thing is, we have tricky brains. That's not our fault. Sometimes we can do terrible things we don't mean to do. And though it's not our FAULT (we didn't choose it in that moment), it is our responsibility to take it very seriously and find a way to learn new skills and strategies to prevent recurrence of these behaviours.
But you know, it's all very much more complex than usually comes across on MN and not a morality play - there are ways and means of dealing skilfully with these questions life asks us of ourselves. When we shame people we activate the internal threat system even further, but what people need to change is to be soothed and learn how to soothe themselves.. and MN is not the best place to do that. It needs to be done in real life and perhaps with skilled psychological professionals.