Bob and I have been sharing works forever. Bob hates my writing but loves my ideas. I guess one day Bob loved an idea so much Bob decided to write it better. I'm afraid to share my most recent work with Bob now. Bob really wants it.
Here in my little suburb everyone is friends and knows everyone. You can't have a critique partner that's not someone you sit with at church. For example, I sent my kids to a sleep away camp two hours away. I didn't tell a soul and fifteen people from my writing group and church told me how much fun the twins were having. Then they all sent pictures.
This isn't a writing problem. This is a people problem. I'm probably not the right person to ask about people problems because I've long believed the world would be better off if I was in charge and everyone had to do what I say. Not for nutthin' does my nameplate say Queen of the Known Universe
I often hear that writing is a solitary pursuit. It seems like you need more of the solitary and less of the pursuit.
While it is true that everyone executes ideas in their own way and what Bob writes will be very different than what you write, even if you start with the same idea, it's just plain rude to ask a writer to see their work in progress. Of course, he's gotten in the habit of doing so because you've let him.
As to how you change this long standing practice of sharing, I do not know. My way would involve something that would probably get you shunned by the community, bless their hearts.
On the other hand, the readers of this blog often demonstrate they are very nice people. I'll bet they have some dandy ideas.