I had this EXACT same problem with my last boy (who was half bulldog). If he was in the back of my ute, I couldn't even pay for fuel without him getting upset at how long I was away from him. If left at home alone, he would pine noisily all day.
I ended up getting a professional trainer friend of mine to help. We did seperation exercises for weeks, where we would slowly increase the time apart and reward him like a bit*h! I also increased his exercise rate by double and eventually it worked.
To this day I have never seen a dog who needed to be so close to someone!
Good luck with your boy. You will solve this problem, but it might be done in small steps. But it will be worth the effort!