A break up really is something you should aspire to get over - however long the relationship was (and no, I wasn't just dumped once at 25- My marriage ended by him cheating, after 21 years together and a child.)
It is in no way comparable to the death of a child, and the fact that you think so is worrying. And no, not even in that you 'grow around your grief' rather than get over it. That is true for the loss of a child, because there is no microscopic part of that that can be viewed as good. Nor did you have any role or responsibility in what happened to you. And the gap can never be filled, even if a future child comes along.
In the case of a long marriage breakup, there are tons of potential upsides.... in being free/ chance to reinvent yourself/ date new people/ have a bunch of new experiences, if you are open to these. It's not a situation that is black and white bleak ... ultimately, if the marriage broke up then by definition it wasn't great in some way. Even if you thought it was great, and he left, you were clearly in some form of denial and/or with a man who was not who you thought they were. And you had a role in making it not great in one way or another, so owning that often helps you get over it. And yes, you can fill the gap of a partner who left you- with a new partner, with different or even better qualities, who you can have a better relationship with.
So, sure - a break up is absolutely grounds for lots of difficult feelings, as you get over it, but it sounds to me like you've become frozen somewhere in the process. I would guess you are either denying your own responsibility in what happened (thus permanently stuck as the victim of circumstance), or you are still idealising your marriage (telling yourself it was such an awful thing to lose it, even though you broke up), or for some reason, you are refusing to allow yourself to be happy?
You seem very keen to put this on other people - their shame or discomfort, or their not understanding. I would encourage you to look to yourself and see if you can change your belief that your relationship was so important that you simply can't get over it..... you're much more likely to end up happy if you do.
Assuming you had your kids with him, then even after 25 years you are likely to have more than that still ahead of you... do you really want to spend it with this loss permanently weighing you down?