You do deserve better, its a shame he waited 6 years to tell you.

Support your girls, it seems as though it was a shock for them as well as you. If anything to keep you going each morning, these girls need a role model right now. That will be you. be open with them how you feel, but talk about the future and your thoughts, ideas, and plans. Include them, make them feel part of your team. Don talk down about their dad, just be open and honest about you.

Show them that its not worth staying in a bad relationship. If he chose someone else, then choose you. Its his loss, your gain