<human>: Give me the gist of the text in a nutshell

Quick rundown... Was married for nearly 9 years, together 13. My ex-wife had an affair with my, then, sister's fiance. I found out and it wrecked my family. We have been divorced for nearly 2 years now. I guess the ex and him have been exclusive for past 9 months and she has started bring him around our 2 children.

The ex and I have a great (well, as good as one through the situation could have) relationship and co-parent rather well. I haven't seen him since I confronted them a couple years ago. If he's going to be a bigger part in my kid's lives, I don't want to be dick to him. I'm over the whole ordeal and if she's happy and my kids are taken care of when they're not with me (we share 60/40 split in her favor) I'm ok with it. 

The thing is, I have to be around my ex because of my children. My family has been around her since and it has gotten better. However, my family never wants to see him again... and I'm not sure what would happen if he was around them.

My daughter is in a parade in a few hours. He will be there, and I will be sitting with them so I can hang with my son for a bit while watching my daughter in the parade. I can't hold a grudge... I mean, if I can't hate two people that ripped my family, who can I hate? Anywho... I don't know what my sister would think if she knew I was sitting with him at the parade... what would my mom and dad think? Should I worry about them? It's my children... my relationship with them and my ex is forever entangled. I can't avoid him and my ex because my family would freak, could I... should I? 

It puts me between a rock and a hard place... I feel like I should hate him, but I'm over the situation, as my ex and myself are better co-parents than husband and wife. I don't think my family will ever get to that level... and might look ill on me if I'm around him. I don't know.... I'm rambling now. 

Any advice??
<bot>: ex cheated with sister's fiance over 2 years ago. He's now coming around our kids. Will see him today at parade (should I?)