About five years of fluctuating levels of doubt, before finally concluding that yes, the relationship was the reason I was miserable, and ending it for good. 20'odd years together, so for the most part it was worthwhile and fun, but the last quarter of it was not.
You only have one life, and the only insight you have that it directly relevant is the one inside your own head, so I struggled for years to resolve the question of whether or not my frustration and dissatisfaction was just what inevitably comes with being in a very long term relationship once the initial spark has dwindled a bit, whether the drudgery of living with someone you know like the back of your own hand was inevitable and universal, or whether it was actually just me being unreasonable and having unreasonable expectations.
As soon as I ended it, like literally within hours, I realised I'd done the correct thing and I haven't looked back since. It was enormously liberating not having to constantly think about 'us' and an individual that I wasn't even sure I really liked all that much any longer.
No kids in my case, so I can't fulfil that part of your request I'm afraid, but I can reassure you that it is not at all unusual or strange to spend years deliberating about the nature of your romantic relationship. I don't really regret not ending it earlier, because although it's clear to me in hindsight that the relationship wasn't really viable for a long time before I ended it, I didn't realise that at the time, so I think it would be a bit pointless to berate myself for not doing something when I really wasn't in possession back then of the knowledge and insight I have now. It wasn't a 'mistake' not to end it earlier, it was just part of a journey I had to go on to ultimately get to the right place to make the decision.