My ex and I have a 50/50 custody-sharing arrangement for our daughter, 10. Our divorce was amicable, and we get along well as co-parents. That involves frequent communication, typically on practical matters.
When dating, I struggle to find people who are comfortable with this. There are usually positive statements at first - it's great that I'm committed to doing what's best for my child, etc - but when we actually get into daily life, it's more problematic. I try to be open and explain my situation - the reason communication is so drama-free now is that our separation wasn't bitter or angry, it was two people who had stopped having any feelings for each other long before we separated. But that doesn't really help. I was even told by one recent girlfriend that she understands I have no feelings for my ex, but that the level of communication itself is the problem regardless.
One thought I've had is that, without intending to, I've dated either women without kids or mothers who have their kids most of the time and have more difficult relationships with their exes. Perhaps somebody in a situation more similar to mine would be more understanding.
For the most part though, I'm really frustrated by this. I'm not willing to compromise on the way I parent; I would rather be alone and do what's best for my daughter than compromise that to make a partner more comfortable. But I would like to find somebody who isn't threatened by what I know as a purely functional co-parenting relationship.