Oh Maypole, your heart must be in knots, and my heart goes out to you.
I had an awful 6 months with my long-term partner, he had been texting someone else, after a period of neither of us being happy, but it wasn't dealt with well. We split, and what ensued was just horrible! We are back together and working so very hard at what we have.
However, it is so hard to trust one another again. We don't have kids, just my baby dog! So no reason to stay together other than we desperately want to make a go of us again.
It sounds like you're being very accommodating, and trying your best to find way of figuring it out. It also sounds like, from your subsequent posts, he isn't i nvesting as much as you are.
You need to tell him directly the way you feel, as he seems not to be accepting the seriousness of his behaviour, or the potential consequences. He stands to lose a wonderful wife and his only child. Think about a time limit, and what you both need to achieve in order for your marrige to work.
Don't make excuses for him, it's difficult when you love someone but don't let him sh*t on you, you sound like you're making such an effort, so he'd damn well better recognise that and reassess his situation sharpish!
Be strong
x