Maybe he doesn't know what he wants yet. If he is changing careers, then maybe he doesn't know the lie of the land well enough yet to know what he wants. In which case, keeping his options open is fairly sensible. So maybe he is drained by talking because he doesn't have answers yet (it would be different if he was in a job he was secure in, he'd know the boundaries).
I also think you wanting to be close to parents when you have a child is fairly sensible. and a commute from e.g. Brighton is one thing, Exeter is another.
Could you do something like set reasonable time frames for decision making (not ultimatums). So something like "How long do you think it will take for you to get reasonably well established in a new career?".
The best example I can think of is DH said to me when had been ill for about 3 months that "I sense I have a chance to really push myself forward in the next year or so, it'll be long hours can you just trust me to get on with it". I was like ok , but we have to look at it again at the end of the year.
To be fair to him, he got himself promoted twice and added about 50% to his salary ( a lot of more senior people were retiring and he could see how he could jump a few rungs quickly). He said he wanted to get us to a position where if I was never able to work again (it wasn't certain) it would be ok. And he did it. He worked a hell of a lot that year, at a time when I was struggling a lot with my health and it wasn't easy. But he did do his best at home too, so did I, we just let a few things slide for a bit as well.
By the end of it I was just about breaking. But we did reassess again at the end of the year and then his travel/working hours dropped back massively and it got easier again. And now I have the security of knowing that if I do get ill again it will be ok.