Honestly, it really hurt at first.
I don't want to say "I know how you feel" since that's insensitive, but like, I know what it is like, at the very least. Because you feel not only did the relationship end, but the relationship was a sham from the start, and also, that being a woman, you were never good enough. So it's really, really tough. At the same time, I'm sure he was struggling too and is sad about what he did. These types of relationships happen all over the world, and they end up horribly 95% of the time.
It's a reflection of a society where people don't realize they are gay until later in life, or repress the fact they're gay until they're borderline suicidal. It sucks.
I'm slowly getting stronger, but the hard part is the kids. How the hell do I explain this to 6 and four year olds?
Tell them when they're older. Unless your partner finds a boyfriend. You should keep him in your life to some extent because you did have kids with him. But don't approach the issue yet. Do it when they're around tween years.
Right now just say "mommy and daddy had an argument and daddy isn't here", you know. Bullshit it. "Daddy went away". And then every once in a while, if you ex wants to see the kids and he should be responsible and do so, then you let him see them so his presence is still in their lives.