This is an interesting post for me. Here it is very unusual to crate a dog/cat or use gates inside. I have two dogs one large, one small, if I go out they are put outside in our fenced yard. Generally when I come home, they are lying in our carport waiting for me to drive in. There are rooms inside they are not allowed, but they have been trained to wait at the threshold. Maybe the crate is symbolic of you leaving him, then he gets anxious. Maybe a sedative from the vet may help to aleviate his anxiety and make the crate more bearable, then once he is used to it you could do without the medication.