Information about a Ratero mix puppy

I have adopted an 8-12 month old rescue Ratero mix puppy. He is healthy, friendly, affectionate, house trained and very intelligent but has a very serious problem crying and extremely loud when I try to go out and leave him alone. Consequently, it makes it very difficult to go anywhere without bringing him unless someone else is staying in the house. I left him outside with my son’s dog for a couple of hours one day and who he plays well with  and he seemed to be content with her company.  It appears that he just does not like to be left alone period.  I am living on my own and alone with him mostly and need to go out by myself at certain times without bringing him. Any suggestions someone might have to try and fix this problem and also wondering if anyone has had experience with the same thing. He appears to be very stressed and is shaking when he is left by himself.  I have stood outside, unknown to him, that I really haven’t left and experienced this situation. Please, any  thoughts or suggestions would be much appreciated. This problem has to be fixed and soon while he is still at a young age and learning.