I'm sorry you're going through this. Honestly, it doesn't sound like he is over her. You said he went to spend Thanksgiving with her and HER kids. They aren't their kids? I would totally understand if the kids were between the two of them, but if not, I don't trust that either.

I especially don't like that she was surprised to see you. If he was serious and just wanted to be friends with her, he would have talked about you. The fact that she didn't even know sounds like, to me, he's trying to work his way back with her. If they were really DONE, he would be open about a relationship (I would hope).

I actually left my ex bc of a situation just like this. He was still friends with his ex and they had dated for like 3 years. He lied to me about going to her house. He would hide texts and kept a pic of them kissing in his dresser drawer. He did throw away the pic and even introduced us (still hated her guts) so I would know that she KNEW about me. But I just couldn't do it. People say they're okay with their SO being friends with exes but, personally, I cannot do it. And luckily my bf feels the same way.

Now I am friends with exes whom I haven't seen in years. They are with another person and so am I. And it's hardly a friendship. More like an acquaintance. But less than a year apart after a 10 year relationship....there's no way those feelings are done. I'm sorry but I would probably get out.