Sorry my mistake. You know what they say about "assuming"? Best to you both.
The trainer I mentioned has good points for easing dogs' fears around other dogs. One of his points is that you walk him w/your head up high and keep him going past his fear - in this case other dogs - thereby he looks to you as the head of the pack and he doesn't feel he has to go into protection mode. Only a few dogs actually want to be the true alpha of the pack. They'd rather sit back w/ya and eat popcorn.
He thinks he's one of you? Ah oh. Next step he'll be pushing you guys off the couch and bed!! hee hee
Have fun w/him and sounds like maybe he wasn't socialized properly when he was a little squirt around other animals. Keep him leashed, walk him or run him (if you have in line skates it works great) till he's really tired and then take him around other dogs. If you have to get in between the other dog and Butch who is leashed and firmly tell him "No". This reinforces your leadership over him and makes him feel he can relax to second in command or third in the case of you and your boyfriend. Remember you have to practice this and it won't take long for him to get the idea.
Juni (ps - I'm learning a lot in dog behavior from Cesar Milan.) Makes for a happier relationship between your dog and you.