misdee, tbh, I know nothing about DCM so can't comment on the 'if we'd have done things differently' thoughts. I presume you can get it by exposure to a virus or through a genetic predipostion, and that re: the virus - some people just get a bit ill, others suffer seriously weakened hearts ? (is that about right ?)
The problem with all this is that time travel currently is rather difficult ... so you can't go back, and not go clubbing that night.... and even if you were able to, of course we can't be quite sure that Peter wouldn't have been v. susceptible to the virus at some other point etc. etc.
Now, it's OK to wonder 'what if I'd have got a different job', 'what if I'd have not come in to work that day (I met Peter)', 'what if we'd decided to have the kids later (and he'd got ill first IYSWIM)' etc. etc. but essentially you will get nowhere as it won't change your present circs; you cannot change anything you've done.
Wanting to change it, or have life's story played out differently, is normal. Who wouldn't want a slightly different twist on life and avoid what your family is going through ? I'm sure you wonder about it all the time, I know I would...
... but the thing is, however much you wonder, it won't change this surreal nightmare that you're going through, waiting for his condition to pick up, for him to be on the transplant list, for some poor family to suffer a bereavement, for him to be offered the heart, for the organ to be accepted, for the recovery to go well, for him to return home and for you all to get on with an 'ordinary' life IYSWIM... you can only do the (very difficult) task of looking after the kids on your own, doing the hospital visits, keeping your mate spirited and hopeful (and the same for yourself and your kids obviously)... and waiting, and seeing...
... the task is obviously enormous and stressful. You have been incredible so far, that is for sure. Maybe to fight 'Round Two' you need to work on getting your batteries recharged, as I get the feeling you're running on low... Peter can cope with a few days without his beloved, and of course you can still write, as you do now, but maybe a few hours / day / weekend on your own (or maybe with the kids, I dunno), would be a really good thing, as well as some simple treats for yourself ??? Perhaps that sort of thing would give you a break for just a tiny while, so you can gather your resources, have a think, navel-gaze on life and the future etc. etc. X