Neutered dog dominance issues. Can someone give advice?

[Pam s]

My dog is three and a half he was neutered when he was a puppy (humane society policy) he never displayed any type of dominance issues and is always submissive around other dogs. He did have a small issue with chewing; he only chewed the crotch out of my undies (still don't know why). My boyfriend's roommate has a male dog the same age same size but was just neutered because he wouldn't stop marking the house, since my dog has been around. He stopped marking the house after he was neutered. The problem is that one of the two dogs marked my boyfriends bed after we had intercourse (no we weren't in the bed when it happened). I don't understand why either would do it. My dog and I have stayed over at my boyfriends off and on for almost six months and nothing even remotely similar has happened. My dog had no issue with my ex when he lived with us. I do not give either of them a hint that they are dominant to me. I trained my dog that I am his leader. The roommates dog doesn't do it to his owner after he messes his sheets with his girl friend. What would cause a dog to do that?

Is the newly neutered dog jealous because he just got chopped or is my dog jealous of my b/f?

No there isn't anything sexual between my dog and me
the dogs get the same amount of attention, food, exercise, and treats while my dog and I are over at his house.
My boyfriend doesn't put the dogs before me

any advice would help!