Can I touch my ex's baby belly?
That depends. Do you know the mom well?
Yes, I've known her for quite a long time. However, she would not feel well about it
Even if you want to, you need to ask permission to touch your ex's belly. It would be an invasion of privacy to touch without asking.
I know it's invasive, but I'm curious about it feels.
It is okay to be curious but you still should ask for permission. Most expectant mothers do not want people touching their belly's.