AIBU to wonder if I have left mentioning a third marriage too late?

Bloody hell there are some snidey comments on here. No one knows the circumstances of those divorces and it's no ones business but yours. If you think you should tell him do it calmly, don't make a big deal out of it and see how he reacts

It doesn't mean anyone is a walking disaster, they might have higher standards and decide not to put up with shit.

As OP has said, and all of us will be like this or know people that are like this, she has friends who are unhappily married but stay for the house, the money, the sake of the kids or for the love of the koi carp, who knows but they stay. It could be argued that some people have a lower threshold as to what they will and won't tolerate and get out early. It's not a fault. More people should do it instead of ticking off the years living with an asshole or putting up with a MIL from hell or living with some porn obsessed pot head.

@CosyPinkOtter Stop feeling ashamed. Live your life the way you want to. You and people think it looks bad but that does not necessarily reflect the truth.

Of course you are.

Why do you think marriage to this man will be different to the other times? In what sense did the others "not work out" (that could mean anything) and what makes you think it would work out this time?

YABU, sorry. Not for the three marriages — nobody's business how many times you've been married — but for the year of carefully-worded half-truths.
"I've been married before and my children have different fathers" when it's actually three marriages isn't an oversight that "never came up," it's a sentence you constructed to be technically accurate while steering him away from the real number. You don't accidentally do that for a year. Every time it "almost came up" and you didn't correct it, that was a choice.
The bit that gets me is you're framing this as your dilemma — how do I mention it now without it looking bad — when the actual problem is you've let him build a picture of your life that isn't accurate, for the length of an entire relationship heading toward serious. That's not about your marriage count, that's about what he's been consenting to without knowing it. He's been falling for a version of your history you edited.
Tell him. Don't dress it up as "something I should've mentioned," call it what it is — you gave him an incomplete picture and let it stand for a year because the truth felt awkward. He deserves the correction and the honesty about why it took this long, not a softened non-apology.

Three divorces by 40 would concern me, I have to be honest, if it were a man with that track record.

How long was the longest of the three marriages?

I was pointing out one of your inconsistencies. In light of that, I'm not sure about the rest of what you've said.

My advice would be don't marry again
I'm guessing marriage isn't a good option for you

I misunderstood
My apologies to all

Make up your mind! You've only just said that you doubt you'll get married a fourth time.

It's not actually a big secret, and doesn't really matter - if you had presented yourself as never being married it would be different. But I can see he might be upset if he thought you were hiding it.

Could you just present it as, something has been really bothering me - I realise I never talked about my third marriage, I wasn't trying to hide it, it just never came up and now I am worried you will think I kept a secret from you - and then just tell him everything.

You should have told him from the start. Tell him the truth but don’t expect him to forgive you as the other way round we’d be telling a woman to run! I don’t think you should be in a serious relationship at all when your children have had such a disruptive life with men coming and going. Just focus on your children for now.

I got that from everything you’ve written. Some people don’t seem to get it or haven’t read everything you’ve written properly.

With respect, this is not a good example.

Why on earth would you want to get married again one day? 3 marriages is enough. Just enjoy being with a partner.

You need to tell him you've been married 3 times. It would raise red flags for me - the marriages and the witholding of information.

She's ashamed for having been divorced three times.

People are judging her for having been divorced three times.

She can't reasonably claim to not understand why she's being judged for something she is ashamed of.

I think if a man was married 3x and children with different women, we would all consider that a massive red flag.
op you should be honest with him. And then leave it up to him to decide.

Good for her! Thats the right attitude to have when you’re a walking disaster.