I am glad you're going to get him neutered.

as for the seperation anxiety you need to invest in a crate so he doesn't hurt himself and do NOT make a big scene when you leave!
don't say anything. I know that sounds harsh but you can say something like be good, love you something like that but don't make a big scene about it because his SA will only get worse.

get a kong toy and fill it with cheese or peanut butter or his favorite treat and put him in his crate with the kong when you leave that way he is occupied. crating him is not going to kill him. it just keeps him safe so he doesn't hurt himself.