Flawed is being disorganised, being late, untidy, grumpy, pessimistic etc.
Flawed is not betraying your spouse, your kids, breaking your marriage vows.
I see a lot of What should he have done, stayed in a miserable marriage? No-one is saying that, merely have the bollocks to finish things properly first and not cheat.
An affair is not a mistake. It's a total disregard for a family, for the promises made to another person. And that's before you get to the subject of children being affected.
How many threads have we seen recently where the OP says I'm not happy, I'm having feelings for someone who is not my DH, etc etc... and the overwhelming advice is to talk to DH, not to do anything 'stupid' and to sort it out properly first. Other threads where OP has been attracted to OM, and he's married... the shrieks of don't go there, are still echoing around the halls of MN.
An affair starts WELL before they end up in bed: a thought, a look, a glance, a kiss, a touch. At any of those points one of them at the very least needs to have a modicum of a conscience.
I'm so very sad to see that it's expected of us to just allow such betrayal of a family to be normalised. In the past such behaviour rightly had a stigma attached.
This is not a case of taking someone's last Rolo, this is a decision by two supposed adults to undertake something that could have profound and permanent consequences for children who have no idea what is going on or why.
Why should his first family just have to get over themselves? It's been 5 whole years... surely they've forgiven us by NOW?
OP is literally kidding herself, and some of you are just humouring it.
'Oh there there OP, you felt a bit guilty, pat, pat, it's OK, it's all forgotten now.' Never Mind eh?
Her DD will most likely never really be embraced nor welcomed by the first family, because of the actions of her parents. Sorry if it makes uncomfortable reading, but it's highly likely to be the case.
FWIW, OP should play absolutely no part in anything to do with his prior family, unless THEY want her to. He betrayed them, for no good reason, and should spend as long as it frigging well takes to rebuild their trust and respect in him.