Are you allowed to list with a second agent
Yes, but how without photographs etc
Does your ex actually want to sell?
How long has the property been on the market - do you know, I saw the first thing you knew of it being for sale was finding it online for sale.
Its a strange area for purchasing houses, there are a few others in the price range but all 3 beds, not 4 beds. Anyone looking can also go back and see it was the same kitchen in 2014.
Once you find the 4th bedroom on the plan and then look at the bedroom in the photo, its a decent sized box room and could easily be a pleasant office.
I think for many its the shapes of the rooms, and as you said yourself it wasn't easy to live with.
You need to find a buyer who wants or needs 4/5 bedrooms, live in the countryside and is happy to decorate.