OP, it does sound as though your DH's behaviour is upsetting you. Esp re the skipping off to Australia thing, and not being around for his family thing, I can see how you'd be upset. Rather than judgements about personality though, I'd say it looks like someone who's too stressed to think clearly.
Re breakdown, what you describe rings some alarm bells for me. My DP went through a nervous breakdown shortly after the 2008 crash: he works in financial services, was regularly doing 90-hour weeks, is driven (like yours sounds) by having grown up without much. So he worked like a blue-arsed fly, found it hard to say no to work, and when the crash happened it all just got too much, especially when the bonuses dried up.
If your DH is behaving erratically, struggling to prioritise, taking on too much, and taking you - his nearest and dearest - for granted then he may be near the end of his tether.
Physiologically, if he's been running on adrenaline for some time, that can do serious damage in the long term. It's a biological thing: adrenaline is produced for a fight-or-flight response, but if he's in fight-or-flight all the time, loads of adrenaline is being produced, and there isn't time for it to be dispersed. A build-up of adrenaline could do severe long-term damage to his autonomic nervous system (the stuff that controls digestion, sleeping, sex drive and so on). This is the physiological basis of burnout. It's more common than you'd think, especially in driven, high-achieving people.
I haven't read your other threads, but if you love him and want him to stay healthy look out for symptoms such as:
diminished sex drive
poor sleeping (wakes up early, can't get to sleep etc)
nightmares
panic attacks
disturbed digestion (eg doesn't eat, eats too much, sudden weight gain or loss)
If you start seeing these sorts of things, he needs to do more exercise (helps burn off excess adrenaline), maybe consider doing a mindfulness/meditation course (sounds a bit woo-woo but meant seriously, it's often prescribed to help recovery from burnout) and see a doctor PRONTO. If it tips over into full-scale burnout it will take him years to recover.
Good luck x