Thanks so much for answering my questions. I really appreciate it.
It sounds to me like Robbie is a sensitive dog who is having a hard time adjusting to the new person in the house. Sensitive dogs (and my boy, Vinnie, is the kind of sensitivity..he's actually pouting on the back of the couch right now because I yelled at him for chasing the cat) pick up on changes in the environment super fast, and the fact that his whole world is being turned upside down right now (because lots of terriers are very one-owner dogs, so having a new person in the house is probably upsetting him) is likely causing him some anxiety. The fact he still acts like his normal self at daycare actually makes sense...it's the one thing in his world that has stayed the same.
There's actually a couple things we can try...
First, there are a couple over-the-counter products you can try to help ease his anxiety:
Melantonin is an over-the-counter drug that can be used to treat some anxiety issues in dogs. The dose you would give would be up to 3 mg given orally whenever necessary up to every 8 hours. More information can be found here: http://www.petplace.com/drug-library/melatonin-melatonex/page1.aspx , which includes risks, warning signs to watch out for and other bits of useful information.
Try a DAP collar. These are collars that are impregnated with a man-made version of the dog appeasing pheromone, which is a pheromone that nursing bitches give off to their pups to help them feel calm and secure. It's something that humans can't smell, but it has an amazing effect on dogs with anxiety and other issues. Although you can find them at your vet's office..you can also find them online at places like Amazon.com and Ebay for much cheaper. Just make sure they're DAP brand, as they seem to work better than some other versions.
And I would have your boyfriend do everything for Robbie from now on. If Robbie needs to go outside to the bathroom...your boyfriend lets him out. He walks him, feeds him, waters him and does absolutely everything for him. I know it will be hard for you because you and Robbie have been a team for so long...but you're going to have to remove yourself from the situation when Robbie needs something.
You could also consider having your boyfriend take Robbie to a basic obedience class...not because you want him to learn to sit/stay (because I'm sure he already knows that), but because this will build the bond between your boyfriend and Robbie. Terriers form relationships while working...and this class will be working for Robbie.
Over time...Robbie will realize that good things come from your boyfriend and will be less timid around him.
I hope this helps.