I'd be lying if I said I didn't notice a lot of anger in your posts.
How's that working for you?
I'm missing something about this whole bike seat thing. He bought a single seat. You wanted him to buy a double seat. The bike has a back seat. From what you said, the back seat would have stayed on if the single seat went on...
What's the issue here? That you wanted him to buy a double seat for HIS bike?