And of course Ragman is the model of righteousness, whose wisdom we all bow to, and who well tell you he his has faults (so that he doesn't seem too superior), but not THAT fault
That said, you let your heart get involved in a very MESSY situation, and quite frankly, it will stay messy for some time - the loss of a child, is often coupled with the breakdown of a marriage, and people involved will always wonder if it's not the marriage that's the problem, but the grief they are both going through - so even after the breakdown (and in your case, a bit of relief with you...putting some perspective on his emotions), it can be quite natural for him to want to try again. What do you think he feelings are for his wife in relation to the grief she's going through?
Also, whether or not you think he is making a mistake, you are disrespecting a decision that is very important, and the reason you are doing so is for your own emotional needs, not his.
It may hurt a bit, or hurt quite a lot, but this is one tangled web you should remove yourself far from. Maybe one day he will come back to you, though I'd advise against getting entangled with him again, in any way.