OP,
Allow yourself a rollixing so that you learn from this, build your boundaries and secure them.
That will mean this experience, though painful, will have had some value in your life.
It is a rare person who doesn't have regrets.
Learning from our mistakes is what makes us human.
Take this time to heal and model something very different to your children and they absolutely will benefit from it.
Don't waste an extended period beating yourself up as that will add nothing to your family life.
His children are his responsibility.
You have more than enough on your plate to feel responsible for, so taking on responsibilities for other people's child and feeling guilty is doing you and your family more harm than good.
I would go so far as to say it is these emotions that got you into this situation in the first place, so be wary of them.
User losers seek out empathetic women with poor boundaries and very quickly make THEIR problems, YOURS to solve.
They really are NOT.
His housing issues are nothing to do with you.
If his seeing his children is dependent on random women facilitating it, then it just reinforces what a complete loser he is.
Take responsibility for what is yours and give a hard swerve on what is not.
Better days are ahead for you and your children.