idk, I kinda think you're freaking out over nothing.
If your kids have been getting close to him as a friend & he moves away then it's a normal life experience - people move. DD's BFF moved in the 3rd grade with little warning but I didn't freak out because her mom didn't give me a heads up so I could cushion DD's disappointment. Our best friends moved across the country years ago & while it truly sucks, we've maintained & strengthened our friendships. Other friends have moved & we've lost contact & that's OK too - totally normal.
If you are more interested in him in a dating sense then it all sounds too early for the kids to even know about that or be affected by it. They aren't being disappointed by a man who is filling a father role in their lives, so no reason to beat yourself up for that either.
Whether moving is the right thing for him or not is for him to decide - is it possible you're just projecting a whole mixed bag of stuff between your ExAH's abandonment of the girls & the issues you mention about your own parents not wanting you to move away having such similarity to his reasons for this move?
Either way - it sounds like this has all revealed more to you that you might not have found out about otherwise - maybe THAT's the whole lesson here? That regardless of what he does, he may not be the right fit for your life, in any capacity?
