I seen she added an old bf. He has a kid. She said to him he is cute looks a lot like you. What do u think of that comment?
I think you need to have a chat with your wife.
You are speculating, and it sounds like there might be a bit of jealously there. Nip it in the bud before it festers any more. And by nip it in the bud, I mean get it out in the open.
Consider that maybe it's platonic first, before charging in with both barrels loaded. Saying a kid is cute is normal. Comparing a kid to their parent is normal.
Do you have female friends? Have you commented on their looks, or their children? Did that mean you wanted to have an affair with any on them?
Granted, this guy is an ex. That still doesn't mean she's rekindling something. I have ex's that I still chat to, and would never let back into my life romantically.
The only way you are going to set your mind at ease is to..
nicely..talk to her, as someone you love, rather than as a suspect.