It sounds to me as if work girl hasn't be the first, and perhaps he's been seeing another woman. You need to ask him if he wants this holiday, or if he'd prefer to go it alone from this point. Would he agree to couples counselling?
Have you apologised for repeatedly punching him? It does sound like he has emotionally detached from you and just wants it to be over regardless of whether he has had an affair or not. Would you stay with him if it was him doing the punching?
Reading your title again, it feels like you are excusing him.
However, he's telling you in every way he can that he doesn't want to be with you. He's just gutless to actually leave. (or he's playing up to make you fall in line with taking care of his child, himself and shut up with demands)
Either way, stop trying to fix the unfixable. He is responsible for what he's doing (it's not aliens or another woman).
You can't make him love him. You've tried being good, you've tried being sexy and you've tried being violent. You can't make him love you. This reads like a very unhealthy relationship and one of you needs to make the difficult decisions sooner rather than later.
It may be a short marriage but you've been together 10 years.... that's more than a lot of people stay together. Sadly 'not letting him leave without trying' is just the equivalent of grabbing hold of his ankles as he's trying to get out of the door.... it's demeaning. So let him go, take control and retain your self-respect. You can work something out for your DS's sake but it'll be co-parenting from two locations rather than one.
'Doesn't know what he wants' IME either means 'doesn't know who he wants' i.e he's got alternatives he's weighing up ... and 'I do know what I want but I'm too cowardly to tell you' Either way, it invariably means there's someone else in the picture and you're just expected to sit there being friendly and carrying on as if nothing has happened, waiting for this knob of a man to decide if you're worth still being married to or not..... If you let him be in control of your destiny like that, what's left of your self-esteem will be all over the carpet.
There's something unusual about the way you describe him and your relationship, but I can't quite put my finger on it. Could you wilfully be not seeing the true situation? You appear quite critical of him, whilst describing unacceptable behaviour of your own.
So he's a coward.... so what? Isn't playing it cool just you being equally cowardly? Is it really so important to you that he leaves of his own volition - i.e get dumped - rather than you assert yourself and end this charade?
Sorry but I think your clinging on to something that doesn't exsist any more. By making him stay your not making anything better. If he doesn't love you then going on holiday isn't going to fix that and IMO will make it worse