My boyfriend is married?!!!!

So I started dating a wonderful man about 6 weeks ago. Things have moved pretty quick. We have talked about marriage and things. We tell each other everything and he has so far been honest with me. He's told me everything with his ex wife, how he's divorced, I've met his beautiful 5 year old girl and she loves me! And I love him and he loves me too.
So today I went with him to drop his daughter off at his moms in another state, and drama of course happened. Which I expected. He told the family I was the babysitter, which I understood, because he didn't want to make more drama.
What I didn't expect, though, was that he came clean and told me he is not divorced. They are separated, and have been for some time. He said after today she is signing the papers for the divorce.
But still, he lied to me. It makes me feel like a home wrecker, or a slut, or whatever...
Honestly I'm okay with this fact. I just wish I had known upfront to begin with. What I'm not okay with is he was lying to me.
Now his ex wife's mom and his daughter are coming to live with him. And they don't know he is dating anyone. So every time I want to spend quality time with him he has to sneak over to my apartment so we can do that (and other things). Which makes me feel like a side chick.
Has anyone else been through anything like this before?