Just cause you neuter it will not stop a dog from marking, that is not true. It also is not true that this dog will mark at your house and not at your fiancee's , it probably does, either they are oblivious or they don't care, I don't know.
The dog should be neutered for health reasons and also because in my opinion it is the responsible thing to do. Neutering will help with the aggression a bit.
You need to have one on one time with him and if need be get a trainer . He is going to be part of your life so with some patience and consistency he may become your best friend, ya never know.
I wish you the best of luck.