Can we not call them "The SS", they are not the nazi secret police! SS (without "the") is an okay acronym although technically they are called Children's Services these days, not Social Services.
Fishfingers speaks sense. DV/EA feels normal when it's what you know. Also when you're in an emotionally healthy relationship, your reaction to something of this nature would be different. It would be a total shock to the system, you would typically be extremely worried by such an out of character act, perhaps wondering if the person was ill, feeling wrong footed, unsure as to how to react, with a tendency to overreact because it's so far out of normal. The perpetrator would also typically be extremely shocked, mortified and upset over what they have done, in a different way to how abusers usually react. From what OP has posted about her DP, he might fit into this rather than the more typical abuser reaction, which tends to be either carrying on as normal as though nothing had ever happened or OTT apologies, extreme niceness in order to "make up for it". Sometimes, though, you do get the crocodile tears/self involved wallowing kind of abuser and this reaction is notable by the fact that it is entirely self-centred and focused on what HE may lose and how HE "always messes everything up" (or similar navel gazing rather than actual holy shit I had better change something and doing that) and is not followed by any action, except perhaps a token one, which will be quickly forgotten once the abuser regains favour. The sympathy from the victim is what they seek and once it is achieved they default to one of the more common abuser reactions of carrying on like nothing happened, or being super nice. It is NOT the fact that he has hurt or frightened people that he cares about being the centre of the upset. It's "what he might lose" and "I don't know why" and "Poor me, everything is hard for me/the world is against me".
When you are used to (perhaps "low level") emotional abuse or control then the tendency in this kind of situation is to underreact because it does not occur in a vacuum, it occurs against a backdrop of a kind of constant storm which you're always riding. Balancing how far you can assert yourself with how much it's going to bother them, picking your battles, avoiding saying something outright or going for more underhand methods of communication because you know from experience that it goes more smoothly. Hearing regular low level criticism which is never quite obvious, just enough for you to doubt yourself, and aimed just right so that it is believable because it aligns with your own insecurities. Typically assuming responsibility for tiny accidents and personality flaws of your own, and dealing with them before they even become noticeable, but also smoothing over theirs or excusing or not minding them, because they are "only human". Silently tallying up microtransactions within the relationship and keeping track of who holds the balance of "points" or favour. You assume that this is just the "work" of a relationship and that it is normal, or typical differences between men and women. You don't notice that others do not live like this. In fact, many do, so how others live isn't particularly relevant anyway.
When an argument escalates and breaks a boundary you feel let down and disappointed, and possibly shocked, but it is never totally out of the blue. You feel that you are partly responsible because you could have diffused the argument, or picked a better time to have it. You are so used to minimising or excusing tiny behaviours that you minimise and excuse this one, too - and mainly because you want it never to have happened, which is a totally natural human reaction. So you look for any way to make it not real. You might actually change your memory of the incident or downplay your recollection of it, convincing yourself that it couldn't have happened in the way you originally thought, because that's impossible. If this doesn't work, or in addition, you can effectively mentally make it "not count" if you can convince yourself that they didn't mean it. So you ascribe a gentler intent and assume a misdirected aim, or a poor choice of words, or decide that he didn't know how he was coming across. Or it was drink, or drugs, or the influence of a particular friend. It wasn't really him, you see, if you can blame it on drink or drugs. And if you just remove them then the problem will go away. Except that 99/100 it won't, because it's a very tiny proportion of people who are so violently allergic to drink or drugs that they make them act completely out of character. Even when you are drunk, you still have free will.
I am not talking about the OP or her boyfriend, BTW. I am describing the difference between experiencing an act of violence from a partner in an emotionally healthy relationship vs an emotionally unhealthy, or low-level emotionally abusive, if you like, relationship.
It's important/relevant, because if OP recognises her BF or her own feelings in the second category, then it might be worth a closer look at the relationship as a whole, painful though it is. (I don't expect a comment on this on the thread, don't worry :)) And because it paints a useful picture of what to do going forward. If YOU want to be sure that it won't happen again, and this should be more relevant than whatever SS decide - then it's worth BOTH looking at the entire situation and the different factors which might have lead up to it and whether anything can be done about those factors. Avoiding alcohol is a start but it's not going to be the only factor. And avoiding it only works if it's forever. BF needs to take responsibility, not in a self pitying way, but in a reasoned and measured way, and decide himself if there is anything he can do, rather than having actions decided for him by somebody else (though if SS suggest anything it is worth jumping through their hoops).
Good luck with everything 