I hope you don't mind my opinion, but if you think you still have feelings for your ex, then you will most likely not be able to stay friends. Those feelings will always be hanging over you.
My ex and I broke up years ago, then about 2 years no contact later, he contacted me. I was in a really bad place and really needed support, though I knew he was a terrible boyfriend, but really missed him as a friend. We met up and he tried to kiss me, which I was unhappy about. But after that, the next time I saw him, and because I knew he must still like me (or so I thought) I ended up getting back with him. However he did this just to get me back for ending our previous relationship. It was an extremely bad idea.
Now I'm not saying it'll be terrible like that, but I just don't think the idea of becoming "friends" with ex's who you haven't been able to stay friends with after your previous relationship in the first place is a good one.
I personally would say you cannot meet him. No need to give him a reason, but if you feel you have to, just say that you don't think it's a good idea.
Then you need to focus on your marriage before you decide to seek any other avenues. You need to focus on yourself. When I was with my DD's father, I was only with him for her sake, until I realised my happiness was just as important, as she wouldn't be happy if I wasn't.
Hope it helps. xx